hmm.... I'm trying to think of asexual snails....I don't know for sure what species are. But I would try to stay away from them. Unless you want 3,000 hungry mouths to feed. I am above culling them, so yeah.
Um, I actually don't know... I am not that familiar with other species, to be honest. There is a lot of debate about whether or not some species are truly asexual or hermaphrodites. It is hard to know for sure because when one snail gets into your tank from a plant, it is usually not the only one.
Ramshorns and pond snails are hermaphrodites... All are male and female, but two are needed to reproduce. MTS reproduce parenthrogenetically (self cloning), and I thing they might reproduce sexually as well.
Apples, mysteries, giant ramshorns, rabbit, etc are all either male or female, and require a mate of the opposite gender to reproduce.
Mystery snails are really, really easy to avoid having more than the ones that you want. If they lay an egg clutch at above the water line you just scrape it off and throw it away. They do need about an inch above the water line when they get to sexual age or they will crawl until they find a way out of the tank to be able to lay the eggs.