You should look at the console exclusives they have; Xbox 360 has great games such as Halo and some of the Fable series, whereas PS3 has equally fantastic games such as The Last of Us and Beyond Two Souls.
Personally I would recommend the PS3, although I don't have one, but I know that the online is free, the exclusives are better and in general the online is more focused on gaming unlike Xbox Live which seems to have a general interest in all forms of media. On top of that, everything Xbox Live has to offer is nothing new, Sony came up with a lot of the ideas that Microsoft have monopolised unfortunately.