this

Both are good, if you want more for a full experience you can check out the fandom page of Nier to see more content(books, anime etc.)

Go for this instead, as this is the version of the protagonist that Yoko Taro always had in mind (in Gestalt for father, you don't have Route E/The Lost World novel, neither the Drama CDs and other complementary novels like Red and Black)

This version has new content added (a couple text stories for emil, new ending, new character that was in a side story) so I'd say this, but I have a huuuuge soft spot for Gestalt and it's OST, and dadnier. I just like the vibe of the older game in general but it DOES feel worse. If you dont mind that and like the looks of gestalt you can easily play that instead :) whatever you'd personally enjoy

Depends what you want.

This version of Replicant does include an extra section and plays a bit more smoothly.

But Gestalt has the uniqueness of playing as an older adult man in an action RPG genre full of teenager protagonists.

I think Replicant fits the original intention of some scenes better, but Gestalt has much more unique dialogue between party members since the main character is older and more experienced. So he talks back to his team a lot more than the Replicant child main character, who's a lot more typical in behavior.

(I also prefer the voice delivery and music choices in Gestalt. The Replicant remake/remaster re-records all the dialogue and remixes the music. But this is preference.)

This version,

Especially if you've never played it before.

the performance and gameplay is improved enough to a good level that this game is one of my favorite games ever made. The original, I had too many issues with its performance, and how it played.

Also the sidequests are fully voiced, (these are the worst part of the game imo) and to me it makes them quite a bit more bearable.

These is also a whole extra epliogue.

I do think the soundtrack is a bit better, in the gestalt, and PAPA Nier is worth playing in itself.

But if you have never played it, you won't have noticed the soundtrack difference.