bristle nose prob easiest to find, grow to like 5 inches or something? when they get too big for your liking easy enough to sell to somebody and buy another 1/2 small ones, got mine at about 1 inch if that took them AGES to reach about 2.5-3 inches, in a big tank with no overly special treatment just a wafer thrown in once n a while, theres other small plecos out there aswell, snails may eat plants, im not a snail man but ones ive had apart from assassins have eaten plants
Otocinclus are very small algae eaters, but they can be sensitive.
Agree with creeker's questions. Is this for the 20 gallon tank that you had the question about in another thread? Based on the rest of the stocking you want in that tank, I'd stick to either snails or shrimp. They have a much smaller bioload than fish and are very good algae eaters. Personally, I'm starting to look into getting some shrimp for my own tank. But, I don't have much algae.
Algae can be dealt with through proper maintenance normally or by changing other parameters so that it doesn't come back. Also, algae isn't really a "problem" in and of itself. It is unsightly, but many times it shows up due to ammonia spikes in your tank and that can actually help to keep your fish safe.