The answer is short: Intel is better because it has invested more into processors than AMD. AMD delivers almost the same performance for the same cost, however it is cheaper.
So, if you have money to spend, buy an Intel i7 newest generation. If money are an issue, then try to buy an AMD FX 8300 or the like. When it comes to gaming you need to remember one thing: the single most expensive piece of hardware needs to be the video card. That one pulls harder when its about video games.