I like the bigger Xbox controller because the PS3 controller just feels way too small. I do prefer the PS3's analog sticks too - I like the convex (outward facing) surface more than concave. I bought convex FPS Freeks to counter this.
Anyhow, I'll list off my reasons I prefer Xbox.
- Halo Franchise (My favorite gaming series since Counter Strike, basically the only game I play now).
- Friends. All of my friends have Xboxes for whatever reason - none of my friends have PS3's - if they did, I would have one. I can't play by myself, it just isn't fun.