I owned a Marshall MG15 but didn't particularly like the sound I got. But I have heard a heap of complaints about the entire MG series. I've also tried a JCM 800 and wasn't a big fan of that either.
I can't sit down and try a Blackstar because no store in my city deals with them, Peavey on the other hand. The store that deals with them are wankers. Although I'd like to change amps I think sticking with Line 6 for the moment might do some good. Not a fan of Fender at all. The only other amps I've tried were Orange and Kustom. Don't get me wrong I'd love a Mesa Boogie triple rectifier but I don't exactly have the money for one