Never used the M-Audio Q40's but I've gotta say, the DT770's are the dead-on winner for comfort; by far the best I've ever seen (Except for maybe Bose, but they suck)
The DT770's may have a way better frequency response but, I've gotta say, they'll never be great all-arounders. I only listen to Electronica and Hip-Hop, though, so they're perfect for me. I love the hard-hitting bass, honestly.
M-Audio looks like a better choice IMHO. DT770's aren't really revered as the best SQ for the price.
BTW: Change your signature, I don't think Head-Fi wants people advertising unless they're paying (Although I know you get "paid" for the advertisment)