Just tweaking what TF said slightly,

the 18W Roadstar does a good clean, up to classic rock crunch. Many people say that the clean/just-breaking-up on the 18W type amp is amongst the best they've heard, and they are highly acclaimed as blues amps.
The crunch sounds like a Marshall, as opposed to a Vox, as TF said. For volume, they can keep up with a drummer when cranked, but if you have a loud drummer, they wouldn't be the best choice for clean headroom, especially if your clean needs to be properly clean.
The 36W (being more harmonically complex)
appears to break up sooner, but is capable of giving a good semi-clean chime at band volumes as well. This is a loud amp. When cranked above 5 it roars and gives a proper rock sound - again, Marshall like.
Both of them have Hi/lo inputs, and the Lo inputs give more headroom, and both can be tweaked to give more or less gain. Both can be fitted with master volumes, Power Scaling or both. Not the first choice for Fender-like, clean shimmer, but they can do chimey, ringing chords and picked arpeggios, then full on power chords just by varying your attack.
There's some good clips here:
http://www.ampmaker.com/ak03x.aspCheers! :)