There's really no good scratch protector - even tempered glass is softer than carbide, and there's a lot of carbide in the air, so dragging your finger across a protector if there are carbide particles on it (and they're too small to feel) produces scratches.
Plastic protectors, of course, scratch easily, but at least they offer some break resistance - which glass protectors don't do. (I've heard of cases in which the screen shattered but the glass protector wasn't harmed.) I go with a plastic protector and replace as needed. They're cheap enough that you can replace them whenever they bother you.