I played CoD 1 & 2 on the Mac pretty well. I've seen videos of people running Parallels or other VM software THEN running CoD 4 on their Macs. It's a versatile little system, so I think I'd have to go with the Mac.
Mac's are good at a wide variety of things, but fail completely when it comes to gaming. They make some PC's specifically for gaming. So I'll go with PC's.
I like Mac over Pc but for gaming pc owns hands down! but soon mac will have games being made more and more... Mac will soon flush out all PC products.