I had a friend who's grandpa had a pond with lots of bass and lots of crappie. There were also quite a few green sunfish in there along with the bluegill. Lots of predators. The thing about this pond that made it unique was that it had trees from about 3 feet of water to the shore along the whole shoreline and a good bit of pondweed. Oh, and it had a sustaining population of shiners!
My opinion, lots of structure.