I'm another potential refugee from HTC considering the Edge over the M9. My whole Android life has been HTC & Sense back to the original Evo. My most recent long-term phone was the M7, recently replaced by an M8 I picked up to play with. I like the M8 overall, but the extra height of the phone bugs me (that giant HTC black bar..uggh). I had been looking forward to the M9, but like many, was disappointed to see the M9 is basically the same (style and size-wise).
While I hate to leave Sense and the front speakers, the design of the Edge has been calling me since I first saw it. It is something different, plus it isn't quite as tall as the M8. The somewhat updated TouchWiz looks better than I remember from the last time I played with an S5. My only real concern with the Edge will be battery life, so that will be interesting to track experiences once the phone is released.
Of course, my other dilemma is if I'm finally going to jump ship from Sprint after 15 years when my latest contract ends next month. While their data network has improved a little in my area, voice signal seems to be getting worse by the day. I thought something was going bad in my M7, but the M8 is having the same problems getting and keeping a voice signal. May finally be time to make a move elsewhere, probably to Verizon.