Got D600 to compare to Momentums and what a nice surprise after hearing all that bashing! First impression is quite positive-packaging, build quality, comfort, isolation. SQ is definitely not worse that my beloved D2000. Same goes when compared to Momentums- It won't be easy to choose between them.
The both have a very different sound. I think I actually prefer the D600 due to the excellent midrange detail and superior comfort (larger pads). I thought the bass was a little sloppy on both. I ultimately owned and returned both of these in favor of the V-Moda M-100 which IMO is the best sounding portable in that price range available today.