I like PS3, but is a matter of opinion. Blu Ray and exclusives like Resistance, Infamous, Gran Turismo 5, Uncharted, Metal Gear Solid 4, Demons Souls, and many more are what won me over. I think what won me over the most though is the FREE Online.
XBOX 360 has Halo and Gears of War, never really been a fan of Gears, but I do love the Halo series. XBOX Live is a little easier to find matches in some games, which I think is due to a little larger fan base, but I still have never seen that big of a difference.