Pixel density is important, but I would not call it the determining factor. The combination of processor power, screen black ratio, pixel density, and RAM all are important in the experience.
I've only used Samsung devices, because I like Gear VR. In the case of Samsung devices, VR Heads already has a blog post on this:
https://www.vrheads.com/samsung-gala...-phone-best-vr.
Honestly, I don't understand why people are getting hung up on specs on this. There's too many parts that can make or break a good VR experience.
If I wanted to use a phone for VR, I would pick either the S8+ or Pixel2XL, and I would personally go with the Note 8. The pen is more important to me than a few pixels, but I can still use Gear VR.