A good tier chip from either brand will do a good job. Assuming you go at least quad core, they will not be the bottleneck in a system.
Erm, to clear up what might create confusion, most games do not get much use out of a quad core cpu even today. Some do, make no mistake, but very few games are truly multithreaded, which is what you need to really utilize a quad core processor. What most games do is shunt minor processes off to alternate cores, but they remain single threaded for the most part.
A quad core does give you more leeway to have other things going on at the same time, since your OS is truly multithreaded (as are many professional programs). So while I do recommend people get a quad core these days, it's mainly due to OS utility and added benefit from that considering the relatively low prices. It has little to do with gaming (over a fast dual core) unless you are playing a game you specifically know is multithreaded. Which again, are still rare.
Edit - And I will say that more games are starting to use multiple threads as game engine coding catches up to professional software coding. There are certainly some that are pretty much unplayable on a dual core, especially some new ones, since they're coded to shift more of the workload to the cpu while expecting 4 physical cores. So going forward, sure, quad core at least is the way to go, considering everything. But many games will still play just as well on a dual core as a quad, and will not cause any kind of bottleneck at all. It's important people understand that.
