I heard the DT770 and DT880s before and IMO they both sounded better than the T1 I owned before.
Just wanted to add that the T1 I had didn't seem to have channel imbalance, but they did sound horrid. Nothing like the raving impressions of the T1's "warmth." The T1 I had was all treble with very recessed mids and bass. Not sure whether what I heard was the intended sound or not. FR measurements still show a recession of upper midrange on the T1s. Measurements show a strong bass response, but FR measurements of bass never seem that reliable to me for semi-closed or closed headphones. I'm not sure if some Head-fiers' idea of warmth is still bright since the T1s definitely are measured to have a treble peak or if the T1 I had was a screw up. Through my previous Woo Audio 6SE, it sounded horrid even with the warmest tubes I could tube roll. I heard another T1 before in a headphone store and it sounded warm. It could have been a warm source it was playing, but it was far too different of an experience considering that my DAC is fairly neutral. The T1 I heard in the store sounded good. The one I owned was probably the worst headphone I ever heard.