Nothing against corys, but I'm a loach kinda guy, and particularly fond of yo-yos. The yo-yos and corys will do the same job (scavenge from bottom), and both would be happier in a group of three or four than in two groups of two. Personally, I wouldn't keep both in a tank no larger than that. I'd choose the loaches or corys and stick with just one or the other. Three (maybe four) yo-yos would be fine if you are going to be diligent about routine maintenance and water changes.
One thing probably worth mentioning, though. Yo-yos are not what I'd call "fragile" fish by any means, but they are more sensitive to water conditions than most beginner fish. If you are a beginner and not terribly confident in your ability (no idea if you are), the corys would probably be more likely to survive a big "uh-oh" than the yo-yo's would.
pendragon!