I haven't played Gothic 3 that much, so I might be way off. But I found Two worlds rather nice as long as you don't expect an epic dynamic living world feeling RPG.
I've heard some classify it as the poor man's oblivion. It might feel a bit like it looking at it, but playwise it feels more like some guys sat around playing Oblivion going "You know, this big world is rather...bland and repetitive isn't it? Wouldn't it be great if we made something a bit more varied and borrowed more elements from Diablo with regards to fighting?
I never played Two worlds as a straight up RPG, I might've gotten something completely wrong there. But I had a blast running around a somewhat varied landscape, chopping down enemies, looting their bodies and thus growing more powerful. Just the fact that you can stack identical weapons to increase their strength means you can get one of the most useless swords in the game, combine enough of them and have something which will knock your opponent halfway across the world just felt fun to me.
Gothic III on the other hand, from the bit I played it, seemed okay but quite buggy. I think if you're going in for RPG elements and story, rather than actiony slaughter action, this might be the better choice. Note I'm not that good with any of the Gothic games' combat system to determine whether that's actually a more action than stat based system

GOTHIC 3 BY A WIDE MARGIN (with fan patch).

I haven't played Gothic series after Gothic 2, so I don't know anything about Gothic 3. But I'd choose Two Worlds between these two.

Is Gothic 3 included in the sale? I thought piranha bytes games were not participating in the sale.

I pretty much agree with DrakeFox - Two Worlds is more of an action RPG/loot collecting game, and Gothic 3 has more classic RPG elements. Both games are somewhat flawed, but fun nonetheless.

Gothic 3 would be my choice. If you choose that one, get the community patch as well. It made the game a lot more enjoyable for me.

A quick check would have shown you it is included.

I picked it up yesterday for $4.99. It doesn't show on the game sale page, but if you go to the game page, it's $4.99

Definately G3... even though it's vanilla version is a P.O.S, it's actually not too bad with the community fixes. You'll NEED them.

Huh. Apparently it's now just the Codemaster games and Gothic 1.

Someone in another thread speculated that it may be because both the developer and the publisher for Gothic 1 is Piranha Bytes, while for the other two Gothic titles, the publisher is Nordic Games. It appears they may be correct.

Haven't played Two Worlds, but Gothic 3 is very, very, very good.
Just make sure that your system requirements are decent, the game is very demanding on hardware.

People say Two Worlds is good once you get deep into it. I was nerded out in the first 20 minutes. And I hated the combat. (I have the XBOX 360 version)

Two Worlds Two is on sale at Gamersgate for under $8. That's highly recommended.

I haven't played Gothic 3, but I've heard it's almost like a single-player MMO. So that's no fun to me.

Ive played both and i had much more fun in Two Worlds than G3... as world type goes there close... but the combat was better in TW... G3 is exploitable to where you can quick hit anyone and win every fight... TW took a little more skill and it was just fun....

thou G3 with Fanpatch is a must play in my book, though... they fixed alot of the issues and combat tweaks made it more enjoyable... ^_^

The thing to note here though is that the XBox 360 version of two worlds was horribly done to the point of unplayability, from framerate issues to game breaking bugs to horrible loading times to controller issues as far as I recall.
I am however tempted by Two worlds 2, but apart from being "now working on XBox" and looking prettier, gameplay wise it's supposed to be a bit inferior to TW1, though, having not played it I can't say if that's true.