Ended up with both versions for a while so i thought I'd share my experience.
--The PS3 looks better. It's slight in detail but the overall artistic presentation ends up noticeably improved. Some screen tearing but not bad at all.
--But, the PS3 controls just felt wrong to me, probably b/c I played the first two on Xbox. I just can't aim properly with that thing and kept "zooming" when I didn't want to.
--So, if you think you're OK with the controller, the PS3 version is the way to go.
To sum up. On the PS3 version I was always stopping to admire the scenery but was frustrated by the controller (again, probably just me here). On the Xbox version I enjoyed the game-play more but lost the sense of wonder from the fabulous art work.
That's it. Enjoy. Great game either way.