Methanol is somewhat more corrosive, shouldn't use steel holding tank or fittings unless you can purge them after use. Methanol has the highest energy content per liter, and the highest latent heat (which is what determines how much cooling): 473 BTU per lb vs iso at 335 or ethanol at 364. Straight water is far better at 970, but it doesn't burn - alcohol gives you back some of the energy. Any common alcohol is available at any chemical plant or laboratory supply house (no, you don't want pharmaceutical grade), and most big paint stores. You can make your own system at a fraction of the cost, but you pretty much have to know what you're doing, and the commercial stuff is easy to adjust and uses less liquid for the effect.
