I would lean toward the puffers and pacu/piranha. Offhand I can't think of any other dedicated snail eaters, you'd expect snail eaters to have a strong bite.
I've seen 4-5ft lungfish tear through large Louisiana crayfish like they were biting into limp spaghetti. I've also seen large 3ft puffers clip steel fish hooks as if they were paper. Overall, my vote goes to the lungfish.