Right now, the majority of games only use up to 4 cores, so an i5 is generally the way to go. However, with directX12, games are starting to use more cores, and in a few years if intel doesn't drop their prices, having an AMD 8 core might be better. Will have to wait and see, but for now, the i5 reigns supreme.
Sir_SwagelotAMD 8 cores are actually just 4 cores with 8 threads, so no, intel would still be the better choice. Especially since Intel is coming out with more cores on their business grade CPUs.