Years of keeping all species of sunfish and I can still never tell who is going to be a bully and who's going to be a pushover. In my experience the species with the most potential for aggression are green sunfish, bluegill, longears, and pumpkinseed. Least aggressive that I've had are warmouth, blue spotted, orange spotted, crappie, and shaddow bass. That being said, there are always fish that don't fit the mold. I've had greenies, bluegill, and longears that have been really good community fish as well. Raising fish up from juvies and feeling them out is the only way to tell who's gonna be who in a tank.