Depends on the algae you are trying to clean up. All CUC fit different needs
For a general CUC I recommend snails (turbo, trochus, nassarius) Urchins, crabs (blue leg hermits). These are just a few that come to the top of my head
I find snails to do the best.
I have hermit crabs too, but they don't really do much that I see.
I have areas of rock that develop some gunk, at some point a snail will go there, and after that gunk will be gone.
I had an urchin that worked well for a while but I think it eventually starved.