Although otos are nice fish, they don't keep the glass clean in my experience. There are some green algae that they don't like. The same is true for amano shrimp, who eat hardly any algae from the glass.
My bristlenose pleco cleared the windows within one day, and they have been spotless ever since. She doesn't care for any hair or dust algae on the plants, though.
Nearly as efficient, with the exception of some black algae, are very young chinese algae eaters. I'm not sure whether the problems with them when they get older are worth their consideration, though.