It sounds like a well-soldered joint is the gold (or maybe silver?) standard. But it requires much more skill than any of the alternatives. And a poorly soldered joint is a disaster waiting to happen.
I like Mex's tip about overlapping the wires inside the butt joint connector, if possible. I am obviously no expert, but it seems that the easier it is for the current to travel through the wires, the less the resistance.
In my particular application (a very long ten gauge stranded cable linking my portable solar panel to my battery), I am concerned about minimizing the voltage drop due to the long cable run. This is a bit of an experiment -- it's a 75 foot cable! (A friend gave it to me -- it was just cluttering up his garage.)
I went to my local electronics store (they still exist in some places) and bought butt connectors and heat shrink tubing. I will be practicing with my crimping tool to make sure I can do the job right.
In case anyone is wondering why I would want a 75 foot cable, we often boondock in deep shade and need a long cable so I can put my solar panel in a patch of sunlight.
We'll see if I get too much of a voltage drop, as compared with a shorter cable.
