Deus ex or GTA 4

GTA4

And btw, I'm guessing you mean Human Revolution, state that explicitely 'cos I think most people will assume you're talking about Deus Ex 1

Deus Ex, it's a far better game.

They are both pretty good. I played GTA 4 on Xbox360 and almost finished it. GTA IV is a bigger game with more to do. But I got bored of GTA IV pretty quickly. It depends if you have played the other GTAs or not. If you've played the other ones then there isn't really a need to play GTA IV. I thought the story was kind-off boring in GTA IV.

I just bought Deus Ex: HR the other day. I'm about an 1.5 Hrs into it. I like the story and it has some nice touches. Like getting to pick up big boxes and throwing them etc, although the game isn't as open ended.

I think HR is the better and more interesting game to play, but GTA IV is bigger.

I would go with Deus Ex: HR just barely. I'm enjoying that more than I enjoyed GTA IV. If GTA IV is your first GTA game then maybe you wouldn't be bad off getting that.

Deus Ex: HR surprised me at how good it is. The story I have seen so far seems like a movie plot and not what we usually get in games.

Both?  They're both excellent and super cheap atm.  I prefer Deus Ex: HR as it's more my kind of game (I'm a big cyberpunk fan) but GTA IV will last you longer I suppose. 

I would go for both, but between the two I'd go for GTA IV.

But you already picked so whatever.