Red devils! My girlfriends red devil have alot of personality! You can watch them pick up rocks and move them to another place for hours! jk jk but red devils are the best!
Polypterus Senegalus are wonderful.
They always have reminded me of otters the way they move about.
The other bichirs are more attractive, but none more entertaining.
RTC's are great also, but few people can house one properly.
My friend had a 300 gallon with a Redtailed Cat named Poseidon and he was like an "underwater" dog.
He would come up to be fed and was extremely personable.