I put the three genera up to give you options, depending whatever what might available in your area, any will work.
I have Roeboides because they are common here, and that's what came up in the catch net, and I want my tank to be geographically correct. I also like them because they are almost the same size as my cichlids, so not at all intimidated by them.
They are scale eaters, and occasionally take swipes at the cichlids with their vampire like teeth.
I also like that they are not brightly, or gaudily colored, which would distract from the main focus of the tank, the cichlids,
but still interesting enough in their own right.
You may find that where you live, serpae or black tetras are the only ones with enough size to handle your cichlids, and that are availabler in your LFSs,
If I had an Amatitlania tank (convict genus) I would probably want Astyanax tetras because these are the type tetras more commonly found in the areas same where convicts are found, and "may" be available in your LFS