I opted for the m8. 830 wasn't much better than my 820 but the m8 still had enough negative qualities that I was uncertain of which to get for a long while. I have loved every HTC phone I've owned in the past, and HTC's devices are sturdy, sexy, and have long battery lives (the 820 possesses none of those qualities) so at the end of the day I chose the m8.
That said, you have to be OK with giving up the following:
1) Glance. Dot view is a mixed bag, and the only way to be properly underwhelmed by it is to try it yourself. I will continue to use dot view despite its many flaws, but know that glance is almost unquestionably superior.
2) Nokia apps. I actually have not missed any of them, but that's just me.
Something that surprised me about the M8: The digitizer makes Nokia's super sensitive touch look bad. The M8 works flawlessly with gloves, keys, etc. Nokia super sensitive touch does competently work with gloves but is unreliable with metal and all around just not as nice as HTC's completely unmarketed implementation.