Out of the ones listed in the 1st post, I've owned them all except for the Hifiman and Denon. My comments:
AKG Q701: great mids and highs, but to me, not enough low end. But really, I don't like any of the K501/601/701/702. I actually prefer the K240 Mk II to all of these. And Sextetts too, btw.
Grado RS2i: I think this is my favorite headphone at the moment. I use mine with comfies because I think they are a little bright (and uncomfortable) with the stock bowls.
Beyer DT880: I really like these too. Very balanced, but for me with my slightly larger than average noggin, they clamp a little tightly for long term wear.
Senn's: I don't know, but I've owned all at one time the HD535/555/595/600/650. There is just something about Sennheiser treble that I don't like. (Not enough resolution? Detail? Not immersive enough?)
But everyone's ears are different too.
