I rely on trochus snails. They do a good job keeping the tank clean, are pretty hardy and breed in captivity. I haven't bought snails in years. Nassarius are good sand-sifters, but dwindle over time (particularly if you keep hermits, who'll scoop out the inconvenient soft bits to try on the stylish shell). I think hermits are *way* over-rated as cleanup crew, often (usually?) doing more harm than good.
I also suggest *not* going bonkers and adding 1 snail per gallon to a new tank, or whatever the online vendors suggest. There's no way a new tank can support that much CUC... you'll buy them, and 75% of them will be dead in a month. The remaining 25% will be really well fed though, cannibalistic little horrors