Honestly, before you buy a keyboard, if you have ANY chance of testing out keys, that helps so much, (ex. At your local electronics store, some keyboards might have keys sticking out of the packaging as a "test", try double tapping those and pressing them to see if you like the feel), but I'll give you a basic guidelines of Cherry MX Switches, though a lot comes down to personal preference.
Cherry MX Brown:
Tactile switch, not clicky, MX Browns are the middle ground between all of the other switches, they are tactile but blue, but light like the blacks.
Cherry MX Black:
Linear switch, not clicky, not tactile, MX Blacks take a little more force to press down than the other switches, but are the best for repetitive tapping or APM in RTSes, as they spring back up very quickly.
Cherry MX Red:
Linear, not clicky, not tactile, MX Reds are pretty much a lighter version of blacks (they are the lightest Cherry MX)
Cherry MX Blue:
Tactile, clicky, MX Blues are clicky and are the slowest to spring back up, making double-tapping a little more difficult.
Honestly, I like blues, even for gaming, but it's all a matter of preference.