Hard to say. It's cat specific IMO. Do you plan to adopt a kitten or an adult? If you work with a local rescue, maybe they can help you find an adult that already seems good with others. I'd go with a female if it were me, but again, it depends on the cat.

FWIW, we've tried to adapt a third cat to our two-cat household this summer. It's not working, but I think it's the personality of the cats at issue.