either a group of africans as suggested.. or just about any med sized sa/ca kept alone would fit the bill imo. personally i like keeping singular fish if I want more interaction. but african interaction with eachother can be hilarious at times. The group of africans will likely be abit more tank maintenece then a single medium fish. So something to also consider. But either way you'll need good filtration and regular water changes so it shouldn't be too significant of a differance.