For what its worth, I have tried several pedals for the purpose that you have described (Tubescreamer, Marshall Shredmaster, T-Rex Moller, etc) and have found the best od/distortion is the Xotic BB. It provides up to 30db of boost, and to my ears the most natural and transparent distortion. It also has a very powerful two band eq so that you can dial in whatever tonality you want, but retains the sound of your guitar/amp. check out youtube for some great clips.