Lots of little ones will hit the tight spots in your tank, and work on many places at once. The big ones eat a large amount, but cant get into tight spots, and tend to move rock and other things around.
I have had better luck with astreas then turbos. Astreas don’t right them selves if they fall in the sand but they seem to eat more types of algae. And you can find small ones if that is what you want.
Not sure what snails I have. I have big snails with the domed like top and coraline on them that stay on the rocks and glass. I also have itty bitty adorable snails with normal like shells and they burry themselves in the sand. I notice the little ones seem to not do as much IMO but the bigger ones are cleaning my rock good!