Eleonora
I fear that angels were a poor choice for that little tank, as they grow quite large and can get pretty aggressive toward each other.
Keeping that in mind, here are my thoughts:
Oto: Excellent little guys, clear up algae, quite active, and stay small.
Bristlenose: Mid sized, too messy for such a small tank, less efficient as they grow but do a great job when younger.
Common Pleco: Do a lousy job on algae, get massive.
Chinese Algae Eater: Very poor choice, extremely aggressive and get quite large.
Flying Fox: More of a scavenger, not a good algae eater. Can be aggressive.
Siamese algae eater: Good choice, not too large, good on algae, quite active
Beware: The last 3 are often confused in fish stores, yet they are very different fish. Try to get the scientific name of the fish in the store and double check that it's the correct one.