I personally like PC simply because I can multitask on it.

For instance, in between SF matches (or when waiting for my opponent to pick a character), I can just Alt Tab to read a comic or something for easy switching.

Another reason is that PC can use console peripherals easily, like PS360 controllers, arcade sticks, etc, but the other way around (say PS3 using keyboard for controls) isn't as easy.

And of course, performance is better if you have a decent PC.

Prices are also better overall I believe. Dead Rising PS3 is around 150, PC is (I heard) 110.