Crap is more vulgar because of the definition, But hell is definitely more profane. Personally I would rather let my kids use a vulgar word than a profane word. Fart is also a vulgar word, But that doesn't make it a bad word. There is no stronger version of hell (or other mainline swear words), But there is a stronger version of crap. Although you could make the case for screw being a cuss word, Because the stronger version of screw or frick is R-rated; the stronger version of crap is a PG-13 word.