We have both. So far I like the PS3 the best because you can go onine on it and such and for XBox you have to have the XBox Live thing for it. Haven't played the XBox very much, though.
My son is totally a Sony guy. Even with all the other systems he has Nintendo Wii, Nintendo DS Lite, Nintendo GameBoy Advance SP, PS2, PSP, XBox, XBox360, Nintendo 64...he still prefers Sony his favorite....maybe it's just because it's the first one he had (PS2) and just got more comfortable with it.