personally I see the PS3 giving the 360 a good thrashing this year (as you can see in my sig predictions). Mainly because of the big guns MGS4, KZ2, GT5 and possible FFXIII in Japan. But also because I think the 360 sales are going to start to dry up.
The 360 just doesn't appeal to enough people, mainly just FPS fans. Even though it has more variety in its library than the original xbox, its image as a FPS only console hasn't changed much.
The PS3 has more brand loyalty (in Europe and Japan at least), it also has more variety in its library. I also expect a price cut to $300 in the autumn/winter. I still think price is the only/main reason that PS3 sales have been sluggish up to this point, (not including the christmas boost).