Well, in all the movies I've seen with these two critters (yes, there's more than ONE of each!), the hoppers just hop slowly and strangle you, whereas the heads fly fast and rip you throat out-- And you can stop the hoppers with a rune on a piece of paper over their faces. So the heads are a lot more dangerous. (The only thing is, there's usually a lot of hoppers, and just one flying head.)
The whole "flying heads with their guts hanging off them" thing is a standard Asian bogeyman. I guess it's marginally weirder than the Chinese hopping vampire, and certainly more threatening.
