Well, According to some research (but no real-world Experience), i would say get the Intel i5. AMD has a reputation of building CPU's with a lot of cores, and unless you do a lot of heavy video editing/rendering, 4 cores would be enough.
Anyways, only some games use multi-core processing. Others rely on gpu somehow. But the decision is up to you!
+1 Core i5 3570K. For those who know me and have me do their builds, you’ll know that it’s just about the best processor you can get for the money today. With plenty of performance, top notch overclocking capability and enough horsepower to run any game you throw at it, the choice is a no brainer.