Well since you never specified one system for microsoft, for me they are the winners. A few key xbox exclusives alongside a ton of great pc games, especially rts.
If we go by console only, obviously nintendo first. Then just from my perspective its xbox and finally playstation 3.
When I had an xbox 360 I probably played exclusives 40% of the time and multiplatform 60% of the time. The few exclusives the 360 did have had incredible replay value to me. I probably played halo 3 alone more than the total time i spent on my entire ps3 library. Forza 2, Halo Reach, Halo Wars, Viva Pinata, Lost Odyssey, Fable 2, and Crackdown were all huge timesinks as well. The ps3 games I spend a ton of time on are infamous and multiplatform.
Now that I only have a ps3 I play exclusives around 15% of the time and multiplatform 85% of the time. Sony has some great exclusives. Problem is my favorite ones are third party that didn't sell too well and so didn't get sequels. While their first party lineup which I mostly don't enjoy is getting milked as much as the microsoft and nintendo exclusives I do enjoy.
