Another vote for Orange my AD200B simply amplifies the sound of my bass without any other additives or fillers.
Except it has a Fender tone stack in it, making it mid scooped with all knobs at noon.
I own and love the TerrorBass 500 which has the same preamp in it. I just crank my mids and keep treble and bass at noon or lower, and it's close enough to "flat" for me.