Of course if you want to use facts and professional opinions on who will have the best line up regarding those games ..
360
Halo 1,2 & 3 - Metacritic 94 - 97
Sales - 6.4 million - 9.6 million
Splinter Cell 1,2,3 & 4 - Metacritic - 85 - 93
Sales - 1.07 million - 2.93 million
Forza 1 & 2 - Metacritic - 90 - 92
Sales - 1.01 million - 3.98 million
Left 4 Dead - Metacritic - 89
Sales - 2.19 million
PS3
Uncharted - Metacritic - 88
Sales - 2.34 million
Ratchet - Metacritic - 62 - 91
Sales - 0.13 million - 2.93 million
MAG - New IP
Demon Souls - New IP
As far as reviews and sales go, this swings in the 360 favour. Of course we don't play sales and reviews but they give us a good indication of how good a franchise is.