No puffer is safe with snails and crabs, although I agree that a Valentini or another toby/sharpnose puffer is your "best bet."
My Valentini, Diddy, has ambushed every snail in the tank, as well as almost every hermit. The hermits now know to stay out of sight till nighttime, when Diddy is sleeping.
My Coral-Banded Shrimp isn't bothered by him, but then again, he only really comes out at night, too.
A puffers natural diet is shelled things, so it shouldn't come as a surprise to anyone that they take a chomp every now and then on the "clean-up crew."