Do you like the Sony or the Microsoft exclusives?
Do you want/need a built in Blu-ray Disc player?
Answer these 2 questions and you have answered your own question.
I've owned a 360 and a PS3. In the end I sold my 360 for no other reason than I couldn't fit 2 big a$$ consoles under my TV and the PS3 seemed like the best bang for buck for me (built in wireless, Blu-ray player, easily upgradeable hard drive, region free gaming, easy Linux installation).