My iPhone, the screen protector is irrelevant, as first thing I do is get an Otterbox Defender case, which has one built in. I thought about going with InvisiShield or Ghost Armor, but I like the protection against drops, especially when I'm at a renaissance faire during rehearsals, and there is a chance the phone might drop onto rocky ground when taking pictures.
My Android phones, I get a decent case, but usually a screen protector comes secondary, especially because Gorilla Glass 2 or 3 does its job quite well. No cracks, deep gouges or visible scratches, although I'm sure if I look at it in the right light, maybe some faint scratches might show up... but I tend to be fairly careful with my devices.