Depends on what you want them to do. Nassarius snails do a completely different job than Astrea's for example.
For general algae grazing, I like the Astrea and Trochus snails.
For removing uneaten food and other items off the bottom of the tank, I like the Nassarius and Cerith snails. These guys are great little scavengers. The Cerith will also get on the glass to help clean that as well.
Hermits are good for both getting uneaten food and removing algaes from the tank. I think the Scarlets are the best out of all of them, IMO
If you use the search function and type in "snails", you will find an abundance of information on ths subject. More so that we could probably provide in this thread.