I was unlucky with the reliability of my Markbass head or I may well have said it was the best I've tried, its impossible to say.
I've only had four class D heads, Bugera Veyron, MB 800,TCE 250 and Orange Terror 1000.
The best, hands down was the Orange. Unbelievable power, clean as a whistle unless you cranked the gain (which you could hardly do unless playing Che Stadium) responsive tone controls.
Awesome bit of kit.