I will never ever buy a phone without a fingerprint scanner on the front. It might be under the screen or a separate button, I don't care. It just has to be, and it must be on the front side.
Of course, I speak from experience. I had a miserable week of using a phone with a fingerprint scanner on the back. Front-faced scanners allow unlocking the phone while it lies on the back, without lifting it. Rear-faced, not so much.
> Having the scanner on the front of the phone means you need 2 hands to unlock it...
Why is that? I almost never use my 6.4" phone with two hands, and my thumb rests naturally on front-facing scanner. Anyway, YMMV, but rear-faced scanners made me very miserable, so I will stay away from them, and face-unlock-only devices.