Both Bluegills and Crappies are in the sunfish family, as are Largemouth Bass.
I guess its really a matter of personal preference. Rick Z here is the primary "fish manager" of a good number of farm ponds in his area. In case I'm incorrect in any of the following (or preceding) statements, I hope Rick will chime in to correct me.
I believe Rick has ponds that have large bluegills AND large crappies, along with the bass. The key seems to be actively regulated harvest...as the harvesting helps ensure there is plenty of natural food available for the remaining fish, which then display excellent growth rates and large average/maximum size.