Here is my philosophy:
Good games come out consistently for Nintendo systems during their entire run, so much so that you have to choose your priorities because of financial issues.
A few great games come out for the Playstation systems (KH, Jak and Daxter, Ratchet and Clank, etc.), but they're so few and far between that it almost isn't worth buying the system.
Xbox has a few good games: Halo, Halo 2, Halo 3, and... um... Halo. That series is really the system's only selling point. Besides, who needs Master Chief when you have Samus Aran?