You guys need to check out the new translucent glass products like Zagg's InvisibleShield Glass. I have it for my iPhone 6 Plus. It is absolutely remarkable. Zero touch sensitivity loss to me, zero optical issues (it's glass) and zero extra finger drag that I can detect. And, it seems to clean way easier and better than the iPhone screen by itself. I really love this product and have generally not used screen protectors before but with products as good as this, I just may change that going forward. I like knowing that my keys, coins, etc. can no longer scratch my screen.
Just ordered a similar product from a Canadian company (InSkin) for my Lumia 1520 which is on the way. Can't wait to compare it to the InvisibleShield Glass. If it's even in the same ballpark, I'll be very happy.