my red spotted sunnie is pretty mean, will not tolerate any other fish, nor will it allow plants to become rooted (it relocates them constantly)
I have tried several times over the past two years to put catfish, and other sunfish in the tank and it has never worked out.
Most sunfish have about the same mentality as Oscar's, and are of equal intelligence, some smarter or dumber (for example they can be trained to eat most prepared foods easily, they will quickly get to know who feeds them, recognize food containers etc)