Since the viewing angle seems to adjust automatically in a daydream headset I'd think the pixel density would not be trivial if VR immersion is one of the most important factors in your phone purchase. For me it's screen size, so I'd get the XL anyways, but for many other people pocketability or one-handed operation are just as important. Remember, even if you adore VR and use it every day 80% or more of your phone interactions will still be as a phone rather than a VR device, so be sure to get the size that you want to carry around with you all the time.
10-15-2016 10:20 AM