I've had a gt200 for a couple of years almost. In the past i've owned a mesa boogie 400+, an orangeAD200B and a fender bassman 135, and i've played on an SVT a few times.
They are all vastly different both in tone and operation. They all sound gorgeous in my opinion. The orange gets closest to the matamp in sound, but still is quite different. The orange has a linear gain knob, whilst the stock GT200 has a 'click' gain knob.
The matamp breaks up nicely and will deliver the 200watts clean before getting into breakup zone. It's a really loud amp. And heavy.
I've hammered my amp for two years and it's going strong, no issues whatsoever.
The only minus I can think of is that I can't afford a GT400 haha not that i'll ever need that kind of headroom, and that Huddersfield is a long long drive from where I live!!! Beautiful part of the country though!
Matamp for me are the be-all and end-all, superior tone, build quality, excellent customer service and quite simply, they rock.