For the past few years, I've been using banana connectors to connect my speaker cables to the Acoustats. It finally bugged me that, despite reasonable high quality bananas, with hefty solid metal connectors (it's the Radio Shack brand but identical to another well known audiophile brand) they just were not being held very well by 5-way binding posts on the Acoustats. (The culprit, IMO, are the 20 year old 5 way binding posts on the Acoustats, not the Radio Shack plugs.)
Actually, I was listening to a classic recording on DVD-Audio when I thought to myself "this sounds grungy" so I looked around for something that might explain the grungy and noticed that one of the bananas in one speaker had come a bit loose and was sagging. This was actually happening fairly often, but I just kept plugging the jacks. But this time, because of anger at the grungy sound, I finally removed the plugs from the speaker wire and plugged the bare stranded 16ga speaker wire straight into the hole in the binding posts (not easy to do even with a bright original style Tensor light, no wonder I hadn't done this before). The sonic improvement was astonishing, much cleaner and sweeter sound.
Another Equipment Upgrade Unit (EUU) in performance was achieved.
Many audiophiles do not realize that under good conditions, well fitting banana plugs and jacks are among the best available connectors. But they have to be well fitting and inclined to stay that way...that is the point.
First consider the spade lug. I do have some experience with spade lugs, and I do not like them for connecting to speaker binding posts. Even when the binding post is tightened down with a wrench (I used to use pliers on the sturdy posts on my Macintosh ML-2 speakers) they eventually come loose. When they come loose, they are among the worst possible connections, and you might not notice it for awhile. Spade lugs work best when their rotation is constrained by the connector, such as with a binding strip. When their rotation is not constrained, they can twist loose and loosen the binding post in the process. Now it is also possible to constrain the cable itself so that it doesn't put any torque on the binding post, but that is generally possible only with low profile equipment such as amplifiers and not possible with speakers which have their binding posts a foot or more above the floor.
A well fitting banana does not have this problem, the spring tension of the plugs keeps it tight, and rotational torque cannot loosen the connection. The main factor here is the proper design of the jack. My Revel M20 speakers (bedroom and kitchen) have nice unbranded 5-way connectors which look like midline WBT's. The inside hole is a straight cylinder (possibly with the outside being slightly smaller in diameter than the inside). Any kind of banana, either the low curvature ones in the late Pomona style, or higher curvature ones which include the Radio Shack audiophile grade, will fit into this connector (though it takes considerable effort to get it in there, at first you may wonder if it's even intended) and stay tight. Only problem, if you consider it a problem, is that the heavy metal binding posts on the M20's are too far apart for double bananas, so you have to use single bananas.
The Acoustat binding posts, OTOH, seem to have a ridge somewhere inside the jack. That might work for the low curvature plugs (haven't tried this), but it definitely does not work for the high curvature plugs I use. What happens is that at the point where the ridge contacts the plug, the plug metal is still curving smaller rapidly as it goes inward. That means there is constant outward mechanical force on the plug, and over time, given vibration, the plug will get pushed out. In fact, I can and did feel that it wasn't gripping very well the first time I plugged my jacks into it, I just chose to ignore this detail to get right to the music listening.
Well, I'm not going to ignore this any more.
Two other kinds of connection deserve mention. One is wires that are terminated in a post which can fit through the hole in the binding post. This is a good solid connection, but it requires a post which is small enough, and binding posts that have a hole (the binding posts on my Krell amplifier do not). Another connection is bare wire around the post (what I generally do with my Krell, despite their recommendation to use spade lugs). Bare solid copper wire is relatively soft and can often hold such connections OK, but stranded wire is even better for this, as it has many degrees of freedom which provide extra springiness. The problem with stranded wire is that you have to be careful that all strands are being held tight and do not come in contact with unintended metal surfaces.