It's not much of a secret - you just pretty much look at the prices.
This THG article can help: Best Gaming CPUs For The Money: August 2010
They suggest Phenom II X4 955 @ $160, Phenom II X4 965 @ $180 or Core i5 760 @ $210. (or Core i5 750 @ $195)
The 955 BE was the best gaming cpu AMD released, due to it's great price and performance. It's equal to an i5 750 in most games, but sometimes some games really favour the intel cpu and that skews the overall results.
I would recommend you check out the individual benchmarks for the games you play then make your choice, but truthfully both cpu's are so close together in performance you will be much better served buying a faster graphics card.