it's interesting what people have said about rats as i've had a few, and modded a few and i've only ended up disappointed with the tone. i found the reutz mod to yield a too 'farty' sound, and although the turbo rat certainly cut less bass, the distortion was too fierce.
my current tweaked rat is a turbo rat that was modded by silent fly for better bass response, but then further modded by changing the clipping circuit to a mosfet and a silicon diode. it's nice and touch-sensitive, but i'd like to eventually tweak the gain control to give a better sweep at lower gains.
having said that, a rat blended with a clean signal to keep the bass is pretty darn good.