The choice really is depending upon what you play. The choices are both nice. If you can live without Dual Rec tones then certainly the Mark IV is the clear winner. If you want the Dual Rec tones then the T-verb is the clear winner. If you want tight and articulate then you want the Mark IV. If you want slightly looser and deeper bottom then you want the T-verb. If you want cheaper tube service you want the Mark IV. If you want a graphic EQ then you want the Mark IV. If you want Mark lead tone then you obviously want the Mark IV. If you want MOP/AJFA/Metallica tone then you want a Mark IV. T-verb is easier to dial in tone with than a Mark IV. A Mark Iv has more versatility though once you get accustomed to its many options. The T-verb is pretty much stuck with its power options whereas the Mark IV has more options for power.
Have you played either one?
I like the Mark IV better. I got a Dual Rec for when I need that Rec sound.
