I prefer the M80s over the Amperiors and DT1350 I own. It definitely bests the Amperiors in terms of mid-range response; vocals come through clearer and are more defined. The DT1350s as I mentioned before, have this weird quirk to them. They sound incredibly thin when left unsealed. Their sound quality is entirely dependent on fit and positioning. At least with my ears.
I've tried various unamped portable setups and I would say that the M80s synergizes best with the HM-601 and Sansa Clip + players. The characteristic that would best describe these setups would definitely be full-bodied. The amounts of bass and vocals from them are deeply satisfying. I'm used to treble-centric phones but for some reason, I'm satisfied with what I get with the M80s. As of yet, they're my favorite phones.