Per random request of a single person, I'm redoing the classification thingy I did for SotFS for DSIII. Honestly, DSIII PvP lacks that level of depth - greatly coming down to basic spacing and R1s - so quality might suffer a bit. This guide/classification/whatever thingy is designed to be somewhat objective, but expecting a completely unbiased evaluation from someone with Illya on their avatar is not the safest bet to make.
Orns already did somewhat similar thing, but it's too focused on salt and is kinda off point in general.

First of all, Dark Souls PvP, even with all the broken parts and metas, is more about understanding and outplaying your opponent than outgearing them, and this guide would be much more focused on playstyles and universal options both in adversary's behavior and countering options. If you want to pull out a new weapon and swap your ring setup for every duelist you see, don't do it - but it won't make you advance your skill at the same rate as figuring out a counter with anything against everything.

Classification thingy is focused on RSS duelist's (and NOT invaders/invasion hosts) playstyles, general approaches to combat and build building within duels, mostly ignoring their behavior outside. Quitting, running into enemies, summoning phantoms - not a fighting style.

Guide is updated to reflect the game stare for 09/16 closer.

- The PvEer
"Oh, there's a Red Sign Soapstone in the game!"
Looks like: usually Knight/Fallen Knight/Abyss Watcher set, a simple weapon and a shield
Fights like: if you were a mob. Walk up, spam, block, attempts on roll backstabs. Doesn't try to be unpredictable or to bait your actions. Can chug.
Threat: Low
Howto: The easiest thing in the world to read and exploit. Outrange, catch, parry, guard break, anything. Chances of meeting a true PvEer are quite slim, actually.
Reward: 100 GGP

- Spamking
"...15678, 15679, 15680, 15681, 15682..."
Looks like: a humanoid holding a thrusting sword or straight Sword in one hand. Some more advanced individuals use Hollowslayer two-handed for hyperarmor.
Fights like: R1R1R1R1R1R1R1 - - stamina recharge - - R1R1R1R1R1R1R1R1
Threat: Medium
Howto: Read. Parry/outrange/interrupt/outhyperarmor/wait out and punish. No real way to get through the spam if you get caught by it other than 3rd hit facetank 8-frame parry or a reverse-roll attack with good range.
Reward: 150 GGP

- Turtle
"T-t-that's a scary p-p-person, I'll better h-h-hide behind t-t-this shield..."
Looks like: something covered from your sight by a greatshield
Fights like: Waits for you to bash at the shield for a while, then does a single counter or spams, or circles you for backstabs. Do not confuse with two-handed greatshield users.
Threat: Low-Medium
Howto: Bait parry or interruption counter - after you do several attacks against the shield, most players would think you're out of stamina and start attacking - dropping his guard, which gives you the opportunity to interrupt that attack with a delayed R1 - on prediction, you can't do that on reaction for most weapon matchups - or parry it. Or bait out both counters and blocking to drain their stamina and guard break, as as anyone who relies on one powerful technique becomes too dependant on it, and so doesn't watch the stamina. Or just bleed them dry.
Reward: 200 GGP

- True novice
"So, what end of the sword is the one to hit people with?"
Looks like: a PvEer with a popular PvP weapon
Fights like: someone who tries to copy the ways their asses got handled to them, copying most basic and popular techniques, or tries to come up with something of their own from no basis. Can try weird stuff.
Threat: Low
Howto: Again, easily outplayed, as those guys usually have quite a limited number of techniques they employ - poorly spaced R1s, basic combos, obvious parry attempts. Fight them like any normal player and don't expect them to play it smart.
Reward: 150 GGP

- True mid
"Draw!"
Looks like: a person in a random fashion set with popular PvP weapon, usually buffs with spells or consumables.
Fights like: Well... normally. Basic mixups, simple baits, tries to read you, usually thinks in patterns, can somewhat adapt, but will usually try to spam something that worked once already, not realising it may only be able to work once.
Threat: Medium
Howto: Hit with that thing in your hands enough times and you'll win.
Reward: 300 GGP

- Reddito
"Oh our Holy Lord of Reddit, please bestow upon us your blessing, and let us reck nubs in Your name!"
Looks like: Fashion of the week holding Weapon of the week
Fights like: what he saw in the latest Oroboro's video. Or whatever youtuber he's worshiping. I won't put people who use established meta weapons normally here, but one-trick trolls like two-handed greatshield users and fire surge spammers do belong here.
Threat: Medium-High
Howto: Meta builds don't become meta without a reason, so his technique is most likely quite broken. But that's just one technique for you to figure out and exploit.
Reward: 350 GGP

- Pokeman
"All right... I'm not scared... I can get close to her... just one hit... then RUUUUUUN!"
Looks like: a person in Artorias set with Washing Pole, two-handed Astora GS, Sellsword/Warden twinblades, Gotthard's, Onikiri&Ubadachi, Claws - pretty much any weapon that has some kind of either hard to punish or very damaging singular combo or attack.
Fights like: Hit-and-run in it's absolute. Run/walk up/wait for your approach, do a single hit or a single full combo, roll away or around, repeat.
Threat: Medium-Low
Howto: Read the approach and counter it. Those weapons are usually used in that singular way. Parry what's parryable and obvious, evade/outspace and punish what's not, or just trade if you know you'll win it. More advanced players often try to mask their approach, making reading it difficult, but as long as you stay on your toes and watch out for it - that won't be detremental. If they do indeed play it smart - they won't fall under this category.
Reward: 250 GGP

- Waiter
"Hmmmm... Quite the pickle indeed. Hm... I suppose I'll wait until it clears itself."
Looks like: someone with a very long spear or Cancer Cuck Sword, though some other fast weapons can be used in that fashion too.
Fights like: he's a gunslinger in the Wild West, or the game simply glitched and won't let them do anything until you take and action, and that action they will try to parry or punish. After success or failure - return to waiting. May occasionaly try doing obvious baits way out of range.
Threat: Medium-Low
Howto: Bait out or put extreme pressure, watch out for roll catches. If you can't really do either with your setup, fighting a dedicated reactive player can be quite an unpleasant experience. Sadly, as they are undead, the most efficient technique - wait until they die of age - won't work.
Reward: 250 GGP

- Baiter
"Come on... Here... Take it..."
Looks like: Either a quick recovery fishing rod or already the hard-hitting punisher weapon, coupled with a parry tool.
Fights like: a fisherman (or an imageboard troll). Throws out the fishing rod, waits for you to take the bait, parries/punishes. Rarely takes offensive action on his own.
Threat: Medium-Low
Howto: Don't be a fish and don't fall for the bait, or put out extreme pressure.
Reward: 250 GGP

- Forcer
"With that many weapons I can't possibly lose!"
Looks like: Slow + fast, zoning + reach, catalyst + melee weapon combos or excess weaponswitching.
Fights like: Tries to throw off your timings and tactics by adding more varied possibilities to his moveset. Usually somewhat aggressive and cocky due to a feeling of safety. Pulling out an Estoc as last resort or finisher is not a real forcer sign, but rather just a tryhardy behavior.
Threat: Medium
Howto: One 'clever' thing doesn't mean you have to forget everything else, but those guys usually don't know that. Read larger patterns. Or just fight normally, as the necessity to think about forced mixups deters from the focus on fight itself. Still, fighting such a person can be quite hard if they know what they're doing, as weapons are usualy chosen in the way to cancel out inherent flaws of either one.
Reward: 400 GGP

- Kirkster
"Why is everything spinning..."
Looks like: an infamous Darkwraith Kirk, usually with a quickstep weapon
Fights like: roll roll roll roll roll roll roll roll roll baby roll
Threat: Medium-High
Howto: rollcatches. With the lag and amount of i-frames can be quite difficult, but you should have enough time with this kind of damage output. If the kirkster is using the weapon too - read and parry/punish, as they won't have i-frames there. A switcherman's way would be to equip Sun Princess Ring and two Blessed items - chances are you'll outheal their damage output.
Reward: 500 GGP

- Scater
"Quicksteps are too cool to take damage in!"
Looks like: somebody with a quickstep weapon, usualy with Carthus Rogue on
Fights like: Quickstep spam + occasional attacks when he thinks he's safe.
Threat: Medium-High
Howto: quickstep catches. As QS have i-frames for ~3/4 of the animation and with lag affecting the equation, doing that reliably can be almost impossible, so the only real way to do it is to introduce random or calculated delays into your attacks and rely on luck to catch either the very small recovery window or their attrack startup. You can also try to parry the attacks, but against a decent player that will get you backstabbed more often than not, as they are naturally circling you most of the time anyway. Poison and bleed do stack through i-frames, but while the former is useless in general, the bleed proc will be just i-framed instead of the buildup.
Reward: 500 GGP

- Tryhard
"Fun is a sin. To achieve salvation, one must win every fight at all costs."
Looks like: an infamous buffed meta weapon attached to a humanoid
Fights like: the video said for that meta. Usually has quite high damage output and/or is almost unpunishable.
Threat: High
Howto: Figure out counters for each meta, it's not impossible. You usually won't be able to reliably beat those by fighting normally.
Reward: 700 GGP

- True vet
"I know what you're gonna do next, kiddo."
Looks like: More-or-less unique fashion, any decent weapon, possible buffs.
Fights like: Usually focuses on reads, spacing, catches and pseudocombos. The overall mark of a true vet is making few mistakes - and painfully capitalizing on yours.
Threat: High
Howto: This is the bossfight of PvP and the test of your true skill, wherever it may focus on.
Reward: 1500 GGP

- Spaceman
"Can't touch this!"
Looks like: Can be pretty much anything, except weapons with neither speed nor range.
Fights like: Outspaces you to the best of his ability, staying just outside your range and punishing whiffs effortlessly and painfully consistently.
Threat: Very High
Howto: This is the most efficient way to play DSIII PvP. Boring, repetitive, safe, requires good reaction timing and memory. You can try to play their game, but if you ain't equipped properly for that and ain't very good with spacing yourself, you won't get much out of it. Playing aggressively, focusing on catching evasions in less obvious ways, can work, but you need to be confident in your timings and watch your stamina while not losing the initiative.
Reward: 1500 GGP

- Honorknight
"By my sword, I challenge you for a duel of honor!"
Looks like: someone fashionable, usually with a rarer weapon, and Untrue Dark Ring for the looks
Fights like: a vet with slightly less options, limited by honor, but no less creativity. Usually doesn't buff or spam supportive stuff like knives. Will probably do 'fancy' less efficient stuff, but in a smarter way, knowing when it will work or is safe.
Threat: Medium-High
Howto: Fight him like a true vet. Honorknights are not exclusively very experienced players, but most of them do first pass through stages of Noobs and Mids.
Reward: 700 GGP

- Hipster
"Now I am not like all of those meta users!"
Looks like: something weird, with a weapon you maybe kinda heard of being in the game somewhere
Fights like: As underused gear is usually underused for a reason, hipster's options will be quite limited, so expect defensive play and baiting/catches. Gimmick playstyles/setups such as hypermodes go here too.
Threat: Any
Howto: Figure out the weapon and deal with him like with any normal player, as they rarely implement singular-dedication playstyles.
Reward: 700 GGP

Tell me if I forgot anything major.
There won't be a 'cosplayer' class, as a cosplay you don't recognize would be completely indistinguishable from another player from a category he falls under by weapon and playstyle choice.
If you have an idea for illustrations that won't be just attaching sample screenshots - you're welcome to share it. I can only think of drawing some myself, but getting one for each 'class' in decent quality would take ages.