generally, snails only eat algae and detitrus etc. Hermits eat detirus as well as left over fish food and algae. Snails can reach everywhere, Hermits can only go to places that they can climb.
I recommend a mix of both types of cleaners. If your aquarium is big enough, you could also have a sand sifting starfish, brittle stars etc. If it is an agressive tank, you could get a sally lightfoot crab etc.
If you want a true mix of cleaners, you could get a cleaner shrimp, green emerald mythrax crabs, or coral banded shrimp. There's just so many possibilities.