I'm in the middle of a Prey playthrough, after completing the Dishonored franchise, and I remembered that I had this RPG from Arkane in the library after a failed playthrough due some big performance issues.

This was 9 years ago (Jesus Christ, lol), Arx Liberatis was an alpha project and there was no fan patch, so I forgot about it, but I think is time to get back in the game, so... what's the best way to play nowadays this game? GoG installation and unnofficial patch or the source port?

GOG install include the new official patch for modern system compatibility and some fixes. "Unofficial patch" is probably not compatible with current version and was deprecated for long time anyway as Arx Libertatis is far superior. Arx Libertatis can be called unofficial patch as well because it only provides fixes and technical improvements and doesn't change gameplay.
I heard AL is still better than this updated release. Not sure but possibly you might need development snapshot to work with 1.22.

So, Arx Liberatis it is.

I see their latest version is 1.1.2 (and surprisingly I'm seeing updates on their github repo a few months ago!)

Pretty cool, I'll try that version, see if anything breaks. Thanks!

1.1.2 may be a bit too outdated.

Here are the latest prebuilt snapshots, if you aren't using them already: https://wiki.arx-libertatis.org/Development_snapshots

Huh, are the snapshots stable? I've always seen them as "in development, for bug finding" and all that.

Good question!

I was pointing to them mostly as an option, because last time I used the release version I ended up having issues which to me were fixed in later builds.
And it seems quite a lot of things were worked on since the 1.1.2 version (5 years ago??): https://arx-libertatis.org/files/snapshots/ (checking some readmes in there, bug and crash fixes are numerous)

I played a few hours with a snapshot some time ago and it was fine - but I've no idea about the whole game.
I intend to replay the game too (just finished Prey last month!), so I would also be interested in how safe a snapshot playthrough is.

Edit:
Well, I dunno if this guy works on the project, but he/she seems to think snapshots are the way to go: https://steamcommunity.com/app/1700/discussions/0/4149469212605682582/

Hmm... I see. A bit chaotic for my tastes, but if that's the way to go, so be it.

Ah, and they even have an rss feed for the snapshots, neat!


EDIT: OH MY GOD THEY ADDED HUD SCALING. I'll stay with this version.