Stainless steel leader wire. The light stuff, I can't think right now the diameter, but it is rated at about 80lb test or so. I use round-jaw pliers for my loops and other small fine-nose pliers for other forming tasks. No need to buy a wire bender. A 25 yard coil of leader wire costs about $4 or so, and will make hundreds of spinners, so cost compared to mono is not an issue. The other problem with mono is that using a correct clevis for the spinner blade will eventually wear through and weaken/break the mono. There are plastic quick disconnect clevises which the walleye guys use for crawler harnesses, but they are not well suited to small trout spinners.
To the simpleton, proof does not matter once emotion takes hold of an issue.