I hope it is OLED. As much of a hater that I am against Samsung. The S6 display is brilliant
I want color accuracy, sunlight usability, display longevity without color shifts, and REAL pixels, not Pentile-style cheats that leave a fine checkerboard over everything. Until I've heard of all those OLED problems being sufficiently solved, I want Apple to stick with really top-end LCD and LED backlights and not cut corners Samsung-style.
Those LCD benefits add up to a lot more to me than the black level when the phone is used in total darkness. Yes, in total darkness, OLED black is blacker. I don't even notice, and if I learned to pay attention to it, I still wouldn't care enough to give up color accuracy (which is different from gamut and "looking colorful") etc.
I do think OLED will solve those things, and if they've all been solved and I just haven't heard it, then you are free to proceed with OLED, Apple
(OLED can also offer a wide viewing angle and no edge bleed--but iPhones have been awesome in those regards already. It's also battery-friendly with an all-black UI.... not something I desire on my phone, although it's fine on the Watch.)