TBH, I've kept all kinds of fish, marine, fresh, brackish. eels, cichlids, puffers, oddballs. and if youre looking purely for personality you want to get a puffer of some kind.
small tank? get a GSP, figure 8 or something like that.
100g tank? go marine and get one of the dogfaced puffers or a porcupine fish, if you keep one alone then 100g should be fine.
got an even larger tank, then a fahaka or Mbu would be the ultimate wet pet. but there seems to be a lot of debate as to what size tank you need to keep one.
many members keep them in 200g tanks but some sources say 1000 gallons.
if for some reason you are a most unique individual and do not like puffers, then i would say get a big cichlid. only problem is they don't seem to bothered in interaction. they just want food, or to act aggressive to you. puffers and many other oddball species show interest in their owners without showing aggression or begging for food.