hmmmm.........it depends what you want...
As far as scavenging goes, shrimps and hermit crabs seem to be just as good. I have a cleaner and a coral banded who are always scavenging as well as hermits, they do their job and dont mess with each other...
But if you want stuff to eat your algae, then you want hermits, cause as far as I know shrimp will not eat algae at all. Sure you can get snails for algae but in my experience they leave rocks alone while hermits go for it like mad....
so basically,
Shrimp - scavenger / fish cleaners
Hermit - scavenger / rock and sand algae eater
Snail - glass algae eater
thats how things have been for me, hope it helps ^__^