I know there's a bunch of people here wondering what version to get. Honestly after looking it up for a while its safe to say both are perfectly fine. The first AC had a bit of problems on the PS3 but this time around they are pretty much the same. In the end it will come down to what controller you prefer and all that jazz.
Here's a pretty good comparison
http://www.lensoftruth.com/?p=16415 Please keep in mind that Lens of Truth is super anal about screen tearing and honestly you probably wouldn't even notice the screen tearing they talk about unless you did all the silly kinds of tests they do looking for it. Judging from what i've seen in the video I would say its a tie but like I said they are super anal about screen tearing in the very slightest so thats the only reason they picked the 360 version as the winner.
Anyways I hate dwell on the console comparison stuff considering it always gets beaten to death. Just go buy the game its great. You'll have a good time no matter what version you get.