Clean for days. And days!!!
Based on Fender pre-amps, it can do clean comparable to Fenders with similar power output. Nice reverb too, it if has it. There are nuances between Fender and Mesa but it can be clean and loud.
The big draw back with II and the III is the shared EQ. Some people have a hard time getting tones they like on both sides of the channel change switch, but as a clean platform or a gained up amp, it has a ton of adjustments to get you lots of places. Oh, and their heavy as hell.
While I agree with Budda about Lonestars, if you get a good deal on a Mk III, I wouldn't pass it up. You can probably turn it around for the same price - as long as you don't have to ship it. LOL