Actually, I don't find spades to be all that great. More than once I had spades lose their contact because the posts are often prone to vibrating loose and all of the tension on the cables is on the bottom which aids in pulling them out. I don't use expensive bananas and I have no problem with them at all. When they lose tension, you just tweak them out again with a small screw driver and they are like new, but that only happens if you are disconnecting and reconnecting your gear a LOT. I've been using the same set of bananas for years without issue. Not to mention, all Marantz gear in the last however many years (at least 10) have binding posts designed so that you cannot use spades... Not all posts are created the same though, so some bananas may be a bit loose in the socket.
The reality is, there is exactly ZERO difference between the two electrically.