20/20.
The 6 has a better contrast ratio (1400:1 v 1300:1) than the Plus, if you want to get technical.
I know about the contrast difference, I posted about it recently, but the reason I asked that is because maybe your eyesight is the reason it looks identical in sharpness and clarity of text. I can tell the difference and other reviewers have noticed the same. 326 vs 401 ppi makes a difference in text that I can notice in daily use. I have 20/12 vision hence the question in regards to eyesight. I know they don't give an eye test to everyone who reviews iPhones. I have personally returned phones for being able to see dust or particles under the screen that people with not as sharp vision just couldn't see.