personally i would always have a pleco in every tank becuase i never have to scrape algae off the sides of my tank, and i honestly pity the people that do! I have a pleco and 2 oto's ,but i heard that oto's won't eat the sheets of green algae that get on the sides of an aquarium.
Of course, you don't have to have one, or bottom feeders, but remeber, your "cleanup crew" all do different things.
Cory's mostly eat debri's off the bottom
Oto's are good for soft algae like brown algae and i think, (not sure) hair algae
Pleco's are good for those sheets of green that get everywhere and have to be scraped off.
I am happy to say that i have never had any of this except for inside my filter
and sometimes on the clear plastic that covers my light, water splashes up on it and i will get a little algae growth
HTH