Spades/bananas have soldered or machine pressed connections to the speaker wire, then a relatively wide contact to the post with uniform pressure applied across the contact surface. Both vastly superior to a small portion of the circumference of one (if single wire) or a few outside strands (if multi-wire) speaker cable making contact. And bare wire connection can be partially lost due to unknowingly pulling on the cable. Plus bare wire connection can be much harder to make in tight quarters and bridging across other posts is also more likely.
Forgetting that the composition of the spade or banana matters too. I cut those little connectors off the chassis wire to the drivers and it sounder better just taped on there.
Richard Vandersteen prefers spades, and I would think long and hard before saying that guy is wrong. I do find them to be a pain in the butt; if one is DIY’ing, I have found that the Cardas CPBP binding posts are awesome and pretty much eliminate any chances of a connection working itself loose. In any case though, I definitely would not suggest that anybody lose too much sleep over this question!
I’ve had perfectly fine success with both types of connectors, spade and banana.
Never really ever had issues with bare wire either. You just have to make sure you don’t have any stray strands bridging between the binding posts. Also, you have to snip off and re-strip every so often to get to new, clean, un-oxidized copper wire so the connection doesn’t degrade over time… And it will.
