I know that it's probably old hat to you, but I get rid of smaller snails by crushing them against the glass. Hand picking often doesn't work as there will always be some that I miss, and it often disgusts me! So, I place lettuce at the top of my infested tank overnight and remove them in the morning. I haven't found a coldwater fish that eats snails. To be honest, I've not searched for one. This method always works for me.
Sleeping with the Fishies