I've owed a few boosters and I use the Fulltone Fatboost Version 3.http://www.fulltone.com/products/fat-boost-fb-3
Super clean or you can add a little grit. Separate bass and treble controls if needed. It is rated to give an extra 35db boost. Use as a boost only or drive dirt pedals or tube amps.
I've owned version 1 and it was good but I love the separate bass and treble cobtrols on version 3. I've also owned the Xotic RC bass boost its good but doesnt have as much juice as the Fulltone. The Fulltone is built like a brick with easy battery access if needed. It is great with passive or active basses.