I love my panda corys, but I'm not sure how effective they are at actual cleanup. They don't seem to really eat all that much.
I have a mystery snail that's only about 1.5" across and he's an absolute cleanup machine. He totally "cleaned up" a 1.5" shrimp by himself in an afternoon. I gave my fish too many peas and 4 were just sitting in the corner of his tank and he ate all of them in about an hour.
And speaking of shrimp, they are really good scavengers, too. They'll eat anything, and they don't waste any time finding stuff that hits the bottom of the tank.
Of course, that really depends what you mean by clean up. Hopefully you're not planning on losing a lot of fish and having somebody there to eat them. If you're just talking about algae, ottos are great algae eaters.
Cories are mostly going to root around in the gravel, dust your plants, and genrally try to be adorable.