Spades Verses Bananas?

Bananas for me. It’s an ease of use thing. 

Plating has little to do with the "hardness" of the connector. That is a function of the base metal. If it is pure copper, that will be as soft as you will get.  The plating is so thin it really is inconsequential as far as overall harness in concerned.  Now, an ultra polished surface has less friction and may be a more "slippery" connection.

In any event, the Cardas binding post I noted above renders these issues moot.

I agree with most people here that good bananas are the way to go. You can often slightly spread out the banana & make it fit quite tightly & it will never come out unless you want it to.  
 

I think the primary reason spades come loose, especially with thicker speaker wires, is that inherently, the wire often must make an immediate or pretty quick 90 degree turn to accommodate where it’s going especially on the amp end.  This can put pressure on the connection & eventually loosen. Thus depending upon the application & the specific equipment involved, they can be the wrong choice. 

I used spades for the first 2-3 years of this hobby. But after that it has been bananas all the way. It had nothing to do with sound quality. I personally feel that bananas lock firmly and the contact area if far more than spades. At the same time, if a speaker cable is heavy, the spades contact can become loose over time, unlike bananas.

I like banana connectors but have had a few break when slightly re-positioning my speakers.