Ramshorn.
They'll eat algae, detritus, left over food... dead or unhealthy plants. They may punch a hole here and there in healthy plants but that's really not their preference unless they're really hungry.
Add very little to the bioloda and help keep your tank clean- I say they're keepers. (unless this is a breeding tank- because they would most likely eat eggs).
In the presence of an abundance of food they'll replicate like crazy. Snail eating fish like these snails because they have thinner shells than many others.