Dogmush, there's several schools of thought...
You need decent tolerances to ensure that you actually get recoil reduction (some of the stuff I've seen out there is just laughable - a bore hole you could throw a .308 through, lengthwise, and they're selling it as a .223 brake... And I've seen the things with woefully undersized side ports.
If you are looking to stop climb, you'll need ports on top and sides. If you are worried about blowing up dust, you don't want ports on the bottom. If you're worried about overall accuracy, you don't want an assymetrical setup (the "we blow it out everywhere but the bottom" tactical folks). I'm doing a few different versions, among them your basic spiral (probably the most intrinsically accurate), a large side port model, and one with no bottom ports, but with top ports to stop muzzle climb (gonna be flogging on that one at Knob Creek...).