I think otos would be the best choice for a ten gallon. The problem with snails is that they multiply fast if there is enough food for them. How many fish do you have in your 10 gallon. If there aren't many fish you could put a rubber lipped pleco in there, but that is kind of pushing it.
I have a 5 gallon and when for about a week i got intense sun I had algae covering the walls so much I couldnt see in. Put in a few common snails you find on aquatic plants and they ate it up within a week. I think common snails will be great-dont get too big either. However they do multiply FAST and hopefully you have somewhere to keep the extras?
my only concern with ottos is that i hear that they are very picky as far as water parameters go... our water here at the house is pretty hard and i really dont know how to go about softening it. my dad works for a local spring water company so i can get spring water when i need it but he is allowed to only bring home so much a week so i dont feel like using the water he brings home on my fishtank
and as far as snails go... well right now i have in the 10 gallon...
5 serpae tetras
1 Colombian Blue-Red tetra
1 Vilma's Tetra
2 bronze corydoras(1 is still pretty young and is only about an inch long)
the serpaes, colombian and the cory's are going into the 55gallon im getting in less then a month and the 10 gallons is mainly gonna be an either a breeder tank or most likely a hostpital tank
i have an Aquaclear 20 power filter and a Penn-plax undertow undergravel filter with an Aquaclear 10 powerhead on one side and on the other below the powerfilter i have the tube with the air diffuser setup for mainly aeration
all that works fine and dandy but i still have particularly hard water. and i just heard that ottos can be fussy about water parameters although i could be wrong
I'd say adding another fish won't help with the algae. You have a highly stocked tank which in itself is probably contributing to the algae problem. More water changes and manually removing the algae is probably your best bet