If you're looking for entertainment, I would go with Oscars. I had Oscars for a while, but was inexperienced about the tank size and had to give them up to a LFS. I can't tell you how hard it was to get me to give them up! I dragged my feet on it until they were pulling out all my plants and bullying their tank mates.
They were very sociable, greeted you when you walk in the room and watch you! They're fun to feed too. I guess it could get expensive, but I would just reward them from time to time with treats from our own garden or occasionally meal worms.
As for the looks, Jack Dempseys are flashy, but I still prefer the look of the Oscars, and they have fancy fins, which I'm a sucker for. : )