a 5.5 inch display sitting in a 5.9 inch x 3 inch phone. Edge to edge display, not necessarily wrapped like the S7 Edge but a little more curve than what apple is doing now. And with slightly chamfered edges so we can get a grip on it (similar to nexus 6p).
But if we are talking about iphone sizes that actually exist, I still say the 5.5. Even though I hate owning such a big phone.
Of apple.cojld get rid of at least 50% of the bezel their 5.5" phone would be the ideal smartphone for me. Even with the 7 we are going thinner but not a smaller footprint. Shrinking in the wrong plane imo.
4 inches. If I wanted a bigger screen on a mobile device I'd reach for my tablet. 4.7" is okay but isn't one-handable, and the 5.5" phone just feels awkward in any situation but portrait mode with two hands.
4.7' is the best screen size for me. It's pocketable enough to use with one hand. The galaxy nexus was the perfect phone for me (from a size standpoint, battery was god awful), the 6s makes it the best overall smartphone I have ever owned.