Well, just received my G3 today and I'm in the process of buying new shades since someone stole my old ones, but I still have the clip-on Polaroid lenses lying around from before I got my laser eye corrective surgery, so I tried those while looking at the G3 just to be sure (read it works fine with polarized lenses, but you can never be too sure, right?).
Well, I can confirm it looks just fine, both in horizontal and landscape though it's night now, so haven't done a full noon bright sunlight test, but the screen is ever so slightly polarized making landscape a little bit darker, but I kept rotating my phone back and forth for minutes to see if I was imagining it or if it was real, so it's not a big difference (I use landscape mode for Navigation myself as of late, but either would probably due, really). Seems this aspect should play no part in your decision between the M8 and G3 then, since they are similar in this respect, at least to orientation of polarization.
I have held the HTC One for a while, which is pretty much identical on the outside to the M8 and my own G3 and the G3 is feather light, better screen & camera, replaceable battery (HTC One has the lowest repair rating by iFixit.com of any phone ever, doubt the M8 is any different) and I'm enjoying my 128GB microSD card, the hand-fitting curvature and especially the knock-on/off feature. M8 ain't premium with a case on anyway and if weight makes for a premium feel, then I'll prefer a phone that I can strap on my arm while running and that won't pull down my loose Bermuda shorts