I have owned and experienced on both...In the end, I prefer Xbox 360 because of the control...I mean, the 360 controller design is good to me; it fits my hand nicely, has better grip and feels much better than standard PS3 controller..Some games I played have better control using 360 controller than PS3 controller...
with Kinect accessories, that's another reason why I like 360 much..Only bad thing about Xbox360 is 'need-to-pay-online-feature' a.k.a Gold Membership...

I don't think I wanna talk about the graphics or that kind of thing, but after seeing much of comparison, 360 looks better so far (played on HDTV Samsung)..but to me, I prefer constant frame-rates, no laggy gameplay than excessive bloom graphics..

I like PS3 as well because of its great exclusive games, features and services they had to offer on its console, and much better to offer than Xbox360, but I am a 'pick up and play' type of gamer, so sometimes I don't usually have time to enjoy some of those great features on PS3..
and back from what I first mentioned, I prefer steady, comfort control on 360...

In other words, try both first, then decide later...