I don't care how much a flagship M8 is, the way they already started to ignore it puts me off. Htc just announced some cool picture software for their mid-range and high end android products. No love for their M8 with windows phone. They just announced the stanalone Re camera, that supports every android and even ios devices, but no love to windows phone, not even exclusive for their own phones. Let's face Htc won't give anymore love to their windows M8. They will provide updates on some of their own apps that come preinstalled, maybe port over some new feature from their android phones in the next 6 months and that's it.
You want the updates, the cool new features that will come down the line, the cool accessories and first party support you go with Lumia. I'd suggest however to waith untill january february for the trade shows to happen to see what they will rlease then, another phablet, or 1020 successor, or if not at least the rumours of the next flagship will happen. You don't want to buy the M8, see it being ignored on updates and features, at the same time the others will get some new cool stuff