For what purposes? Algae control? Scavenging?
Algae control wise, nerites are a great choice. But they tend to lay unsightly eggs around the tank that will never hatch.
Sulawesi snails are cool, but I'm not sure what type of care requirements they need.
Scavenging wise, I like mystery snails.
So many fish/plants/inverts to keep, not enough aquaria.