The answer to your question, "What is the difference ....." is that the various alcohols each have very specific chemical characteristics.
-Because molecular chemistry is, after all, the determining factor between, say, diesel fuel and gasolene (etc.), this is what you pay attention to-
For the purpose of detonation suppression, Iso is least appropriate. Forget that.
Denatured has the most btu's, while methanol the higest Latent Heat Of Vaporization. Therefore, if mixed in low ratio, methanol should come out slightly ahead.
In reality it can be a tradeoff. Sometimes you just have to experiment to see what works best for you.
One thing for sure, if you need max knock control, a 50-50 water/alcohol mix can't be beat. It also will give definate feedback when you're fluid flow is too much, thanks to the water. If you use denatured you can then gain back some of the (lost) btu's.