At first I thought my marshall JCM2000 stack didnt have enuff distortion, and compared to the AVT marshall ones it doesnt, but you still dont need a pedal.
With an amp that big when you get it reasonably loud it creates its own distortion.

Ive tried several pedals with it but it took away the great sound of the amp, to be honest Ive been pretty disapointed with almost all the pedals Ive tried. I dont think you can beat the tone of a marshall and the inbuilt reverb.

What amp you got and what amp you thinking about getting?