BD claims to be the most power down low due to their off-set butterfly and therefore no need for pressure relief. I checked them all out and went with the Banks. See the previous threads on the same subject (do a search). The newest model of Banks brake does not use a pressure relief hole like the older ones. I feel mine slowing the truck clear down to 1500 rpm.

Pac Brake is cheaper and seems to work well. I prefer the air activated systems to the vacuum activated. I also prefer a remote mount to the turbo elbow replacements.

I have yet to hear a complaint about any of the big name brands.