I've had my One M8 since May.
I absolutely love this phone.
The only thing I did not love was the lack of updates through VZW. So I got tired of waiting and went with the ViperOne ROM. Took me forever to get rooted and unlocked and S-Off, but I got it and now I'm just fine.
The thing about Android devices is how different each one is. Stock Android is what you get on the Nexus devices. The next closest to stock is the Moto devices Google puts out - like the Moto X. Then after that are the custom ROMs that cut back to close to stock Android - like the CleanROM for the One M8. But of the non-Google devices that run Android, HTC has really done a phenomenal job in keeping the feel of Android without too much bloat. Of course there's always carrier bloat, especially from VZW, but if you root you can remove those items (even with the temp-root Weaksauce exploit, which doesn't void your warranty). For a more genuine Android experience, I use Nova launcher instead of Blinkfeed. But I really, really, really like Sense 6. It's a great feel for the device.
But really, either device will be fine. My girlfriend has the original Moto X, which only has issues because of poor signal in my area from AT&T (hence why I have VZW). But other than that it works really well. If you want the more genuine Android experience, go with the new Moto X. You can always customize anything you don't like.
For Android, SwiftKey is pretty much necessary. Best keyboard bar none.