The Momentum have a more balanced bass while I can tell there are very little recessed bass at the ATH-M50 somewhere around 100Hz. The Momentum also sound more natural, more musical IMO.
If you can afford the Momentum Over-Ear, go for it. If not you can look into the Momentum On -Ear since you are not wearing too long so comfort shouldn't be a problem. In terms of quantity, the momentum on ear offer the most bass out of the three mentioned in this post. It is more aggressive sounding compared to the more "relax" if not, veiled [TO SOME PEOPLE] nature of Momentum Over-Ear. Isolation wise, the AH-D600 did best.
Hope it helps
Billson