I'm not a fan of Banana connectors, but it's simply a personal preference of mine.
Pros ... a Banana has at least the potential to create simple, electrically stable connections that are easy (and in particular, quick) to make and break. Compared to some audio connections (RCAs for example, which has no standard specification), due to the fact that they are derived from those used in electronic lab equipment, they are more dimensionally standardized.
What I dislike about them? Well, even though there are standard dimensions to follow, many audio manufacturers don't follow them with any consistency or precision, so there is no guarantee of a sufficiently tight electrical fit.
What I find to be worse, however, is the physical fit, which might introduce the risk of loose Banana connectors shorting out inadvertently, say, if the cat steps on a speaker cable and the fit is not gas-tight.
A well designed connector should be idiot-proof and in particular short-proof; there are dual Bananas available in the market but HiFi examples are typically two single connectors (for + and -) which can touch, partly due to the longer dimensions.
It's not something spades eliminate entirely, but they tend to be more securely fastened at the loudspeaker end. There is much less need for standard dimension when you can screw down the connection in the manner of a spade and binding post, so typical variations in dimension are less of a problem there.
The mass varies widely and there is a school of thought in audio that says the mass of each mating surface should be as similar as possible. Bananas tend to be lighter construction than spades, and binding posts much heavier than them. You might dismiss that as "snake oil" although certainly it's something that is always taken into account when any connector is designed, so at least the engineers who do that work seem to agree it's important.
When it comes to Audio, the only true properly designed connectors, ones that take everything into account including which polarity makes first contact (to eliminate brief bursts of hum should the power not be attenuated when making or breaking connections, a failure of the RCA connector) are XLR and BNC connectors.
The only speaker connection that maintains the advantages of XLR and BNC is Neutrik's speakON. Again, rare in HiFi, even though it would probably only need to be at the loudspeaker input alone. Perhaps someone should suggest to speaker manufacturers to offer a dual-connection type option, but just like many other superior connection methods*, they would add cost and wouldn't be popular with lower cost products that comprise so much of the speaker industry.
At the higher end, where cost would not be an issue, they are viewed, like many things that come from the Pro Audio segment, as inferior sonically (which is highly debatable, but a manufacturer will go broke forcing consumers to accept something they dislike for any reason, real or imagined).
We have to make do with what we have. Bananas have advantages and disadvantages but they are not perfect, so can't be said to be the ideal solution, although the typical alternatives have their own issues as well.
The "cousin" of Bananas, the pin connector, has the same advantages of spades and meets more closely the similar mass requirement, but they are not a quick connect option, so they have similar disadvantages as spades as well.
Best electrical connection is probably bare wire, but wire can be brittle and break at the connection, especially if it's made and broken repeatedly, or subject to bend stress. Bananas are best if you exercise the connection repeatedly, and spades the best if you only do so occasionally. But in all cases there are advantages and disadvantages.
* The classic cases familiar to most people today is IEEE 1394 vs USB. Both are open specification (no royalties or limits; developed by Apple and Intel, respectively), but there is a difference in the robustness of the connectors themselves as well as the protocols. IEEE 1394 (aka "Firewire") requires no CPU cycles to interface, everything necessary is in the chip itself, so that a camera can interface with a hard drive, for example.
USB does, so if you want to do the same thing, the camera must have a CPU somewhere, yet because the chip for IEEE 1394 cost about two dollars more than the USB chipsets (resulting in a $10 retail price disadvantage), manufacturer's shunned it.
SONY's attempt to mitigate the cost of a six-pin IEEE 1394 by introducing their own, 4-pin unpowered version didn't help, creating market confusion and compatibility issues.
That is the same problem facing the speakON connector. Although speakON is a trademark of Neutrik (just as Firewire is a trademark of Apple) there are generic versions available (called "speaker twist connector").
Note: even a USB 1.x interface can easily handle the required data stream for an audio CD, so there was also no real need for the IEEE 1394's much higher transmission speed. USB 2x can handle high resolution audio and video. speakON has a 40 Amp rating, more than enough for most high powered amplifiers, a higher current version is also available.
