I work terminations mainly with heavily silver plated wire (see feedback under Valueaudio for some comments about our workmanship. If I go with unterminated cable, I feel much more comfortable going with a heavy silver plating or an all silver cable, since conductivity of silver actually INCREASES if it oxidizes. Copper basically goes to crap conductivity-wise if it oxidizes. With copper, it's usually better to give it a good air-tight termination, or tin and solder the ends, most importantly to help prevent oxidation.
The other benefit of termination is that the cable becomes a component in and of itself...detachable, reattachable, without needing to cut off messed up old strands of wire to do the reconnection and get rid of the oxidized mess with bare copper.
Spades are generally better. The metals available to build them are of purer conductivity. Avoid nickle plating, which is often used under gold plating to make it look pretty and shiney. It's poor sonic material.
Bananas often are made of brass, and nickle plating is more common. Some are made of Beryllium Copper, like the Nordost "Z-Plugs" and AudioQuest's similar, but crimpable design. Nordost actually recommends their bananas over their spades for sound...I believe it is because of the lower mass more consistant with the aggregate diameter of the cable. This makes more sense to me at low levels, such as interconnects, where as speaker cables are a much higher current design, which can benefit from the mass.
I prefer a very good solid crimp over soldering. Good crimping leaves little reason to solder, as even the best solders only have about 16% conductivity compared to a crimp. A good crimp makes an airtight connection. Not all spades or bananas are appropriate for crimping only, and may slide off, but a good solid barrel on the spade can make a terrific crimp connection if done correctly. Without spending a small fortune on spades, where the money can be spent better elsewhere, I like the heavy ones from AudioQuest that retail for $15 for four, made with long grain copper and either silver or gold plating. I've not yet come across a better crimpable spade without spending far more. They are a bitch though...takes alot of pressure to put on because they are so thick, solid, and heavy. I've busted a few 8 gauge crimpers over time installing them.
You must think through the process of termination very step by step, or you will find yourself forgeting to slip a shrink tube on before installing the spade...stuff like that. Try it out on some cheaper wire with cheaper spades until you get the hang of it, and control your heat tube shrinking without burning or discoloring it from too much heat. Be careful if cutting through outer jackets not to cut through to the inner insulation around the wires. Their are special tools that can adjust the right thickness to cut.
I disagree with the fellow that thinks a dealer should terminate your cables for free if you buy it and spades. Good termination work can easily take 45 min. to 2 hours per pair, so unless they are making alot on the sale, don't expect a quality job for free.