PS3 is superior for its entertainment aspect, (i.e. movies and music). Also, I think it's better for not having 6-year-old squeakers, and their exclusive games are much better. Also, I like the less-clunky controller design for the PS3. The benefits of Xbox are they are better for gaming, especially with their cross-game chat. Also, since LIVE is a paid service, it tends to be more reliable than the PSN counterpart. With many games, the Xbox tends to run slightly smoother.
These are my opinions, and you can have yours. I personally like PS3 better than Xbox, and PC is superior to PS3.