I've had RCS with a betta before. No problems. Yeah, as you said, depends really on the betta.Another vote for Betta or Dwarf Puffer. Not so sure about RCS with a Betta though. We put a Betta in a 10gal with RCS & he sent them all into hiding. We actually thought he had eaten them all until he got moved to a different tank & all the RCS started coming back out of hiding. Depends on the Betta in question I guess. Can't hurt to try it. At worst the Betta gets a good feed.