I have the Marshall MB4210 which I use regularly with a couple bands and it has never let me down. I sometimes use the matching 1x15 cab for gigs, not for volume but just because it annoys the guitarists! I do know some people have had problems with theirs, but touchwood, mine has been fine.
The reason I chose it over the Ashdown is I just felt it was more versatile and actually had a nicer tone in my opinion. Just to put that into context, I am not an Ashdown hater, and did not think it was "wooly", I just felt (in my opinion) that the Marshall had a better "rock" tone.
See if you can find a local dealer and try them both, it's the only way to be sure!