Re: Which back/material is more scratch resistant?
Those stories are probably by people who don't realize sudden temperature swings are never good for any kind of glass, especially tempered glass. Probably took their phones out of their pockets (where it would be warm) or were using their phones enough to heat up the back and then put the phone on a cold surface, where it "suddenly" and "magically" shattered. Being unable to feel the clearly visible cracks with a fingernail would be further evidence of this.
In any case, I think the ballistic nylon would be more rugged than the other variants. And even if it weren't as tough as the MGF, the texture would certainly hide scratches, scrapes, and gouges a lot better than it would on a smooth surface... this would probably be the first phone that I've seen in recent times that I would definitely have no qualms about using it without a case.