What does the algae look like? Is it stringy, looks like fine hair filaments or sort of sheet like?
Snails are a better choice if the growth isn't extremely heavy. I you have hair algae and a ot of it, you need to try and clean off as much of it as you can to help out the clean up crew you decide upon.
Urchins are neat lookikng critters but they grow quicklly and can disturb things as they move about..they aren't particualrly careful. IN a 10g I would go with snails and/or hermit crabs. The scarlet legged and blue legged hermit crabs are good hair algae eaters and the Nerite snails are good for general algae control.
Take a look at the site called reefcleaners.org. They have a good explanation of the types of snails and crabs and what they are good for in the tank.