Keeping 2 of either sex will work if you want 2 convicts but don't want them breed. Personally, I like the idea of two females better since they have the gold flecking on their bellies. They'll still lay eggs but they won't be fertile. I'm not sure I'd keep cories in with convicts. When the convicts are small it would be ok, but once they start putting some size on, I think the convicts might get a little nasty to the little cories.
I've kept breeding convicts and cories together. I don't know if there's any difference between my cons and other but it worked out fine. If you want them to be less dominat and competing for teritory your should probably get 2 females. for some variety you could get a pink and a striped or maybe a marbled...
What other fish are you planning to keep them with?
Used to be the first Supermoderator on here when the site was first made, but havn't got enough time on my hands now, but still glad and proud to be a member of a great place with a great bunch.