If you want to get technical, a Topre is going to be the best keyboard for gaming since they don't have to wait for the keys to debounce.
Realistically though it doesn't matter aside from possibly staying away from buckling springs and Cherry Blues. Just get something that is nice to type on and has NKRO. I had the I-need-the-best-of-everything mentality a while ago and still got whooped by my friend who was just more naturally talented than me. A good mouse an monitor does make a difference, but as long as all your keypresses register, a keyboard doesn't matter.