I found that both channels were quite usable, but they are quite different. The T channel is very clean, deep, and glassy / icy (if that makes sense...) while the D channel is a great deal warmer and notably grittier. Because of this difference, I found this the most difficult stock dual module to dial in because of the shared EQ, which is not normally a problem for me.
Personally, I'd be more likely to use a T/T, or maybe a D/D. But I decided to have a custom clean module made by Rob, which should be here shortly.
Anyway, hope that helps.