Assassin snails are probably your best bet. Most of the time snails are just a big nuisance, overpopulating the tank. A few assassin snails should keep your snails in check, just wait until you have a healthy population of snails. Assassins are cool to watch too.
Clown loaches and other big loaches are too big and require large systems (55-75 gallon+ minimum), so I would go with assassins, as stated by others.
Snails that hitchhike on your plants aren;t harmful that much, in fact, they can help clean any food that falls into the substrate.