I got a huge hodgepodge in my 46 of different cories. 8 are aeneus (normal and albino). Theres also some oddballs of weitzmani, sterbai, ambiacus, and leucomelas. They do have a preference to be with their own species, but they do all chill together in big cory piles. But if an aeneus swims off, its usually aeneus who follow it. If a leucomelas swims off, the other leucomelas is right after him.
I have 17 total and they do all mingle, but do also like to associate with their own as well.
Its kinda like people with different languages. Sure, lots of people around would make you feel comfortable (unless you are socialphobic like myself), but you would be even happier if you spoke the same language as at least one of them.
So while my bigger tank has a mix, i try to be sure everyone at least has a friend or two of their own. Except the Ambiacus because he is impossible to locate more of in my country unless by total fluke like he was. My smaller tanks are kept to 1 species only for cories.
If you only have space for a small shoal (6-8) stick to one species.
Larger tanks can fit more and theyd love a huge group and gives more freedom to mix if you want to.