The optimal would be pure distilled water with something like Redline Water Wetter added to improve heat transfer. If you see freezing temps in your area though, add the required proportion of antifreeze for the temps you see.
Methanol only has about half the specific heat capacity as water, so you'd see much poorer performance. Maybe you're getting confused with a methanol injection system? Totally different operating principles... evaporative cooling (and octane boost) vs convective cooling.