Heya,
I have both. They're very similar. The main difference to me was that the M80 is better built, it's way more durable, will survive some knocking around, and has a detachable cord. But the ESW9 was nicer looking and more comfortable. It just felt easier on my ears, softer. The M80 is comfortable, but felt stiff and didn't sit on my ears as easy-going as the ESW9 does. Total build goes to the M80 hands down. The cords (thickness, sheathed, detachable), the frame (sturdy, very strong). ESW9 though wins on looks, being wood back, lambskin, and ultimately more comfortable to me.
As for sound, well, very similar. They both have excellent butter smooth mids & treble, no fatigue at all, both have very good bass response. The M80 may have an edge on the ESW9A for bass impact. Both have a very liquidy smooth sound though, very warm, organic sounding. Able to kick some EDM, also able to have a relaxed acoustic session.
Ultimately, I think I like the ESWA better for wearing/looking at. But the M80 really is built to last and will survive some mishaps. So, it's a toss up to me.
Very best,