The AVT and JCM are totally different amps, so it all depends on what you need. I'd say 250 pounds is a pretty good deal though.(if the amp is working properly) With the JCM you end up with less features than the AVT, but an all-tube amp. You decide what's best for you.

Oh, and of course Marshall says their AVT series is great, how else would they sell that stuff? I wouldn't go near those amps myself, no matter how good they claim they are.

ps: all-tube amps aren't better by definition, but many people prefer them because they have a nicer/warmer sound.(I'm one of those people)