The traditional (and pretty reasonable) logic has been that spades offer a more secure connection than banana, while banana is more convenient. It is kind of nice to be able to tighten down a binding post on a spade and feel sure that the connection is going to stay solid for a long time to come. I'm using bananas for my surrounds because it's easier when connecting from the amp to the wall plate that gathers all four speakers' wires together behind the entertainment center, but the mains and center are using spades at both ends.