Referring back to the question of if you only want one snail.. I'd get a mystery snail. They are attractive, don't lay eggs under water, and are very effective at keeping the glass clean. I find them decorative as well, they come in several nice colours. Ivory, blue, gold, purple, near black too. Shells can be striped or solid, gold, ivory or brownish, and any body colour can be in any shell colour. They can live for some years and get to be about the size of a golf ball, give or take. Aka apple snail, but be sure it's not the giant apple snail. That gets to the size of a baseball and eats plants like mad. Mystery snails won't eat plants unless they are very hungry, but they will eat dead plant material, left over fish food and they adore algae pellets or wafers. I have dozens of them, mainly babies I'm growing out, but the glass in their tank is always spotless.
If you end up with a female mystery snail, she might lay eggs, but she'll do it above water and you can scrape the clutch off when it dries and throw it out if you don't want the babies.
Nerite snails are also excellent glass cleaners and I'm very fond of them, but they do lay eggs, everywhere. They can't hatch unless they're in salt water, so you won't have babies, but some folks are unhappy with the little beige dots of eggs all over every surface.