Warm displays are easier on my eyes, but I much prefer cool displays because I notice the yellows/orange tones much easier than the blues. I think my 6s display is on the cool side, but I really can't tell unless comparing side by side with another phone; so I'm happy. My wife's 5s on the other hand is quite warm, but she does not care in the slightest.
Agreed. Warm may be better for my eyes but I like the cool blues much better. It's no different than when I buy flourescent bulbs. I always gravitate towards the cool blue/daylight bulbs over the warm toned ones.