Actually, in terms of the best BTU transfer per given volume, distilled water is the best. However, it has no corrosion inhibitors and it freezes at 32 deg (f)(0 degrees c.).
It's also the cheapest. Ethylene or Propylene Glycol (antifreeze) because of it's chemical makeup is less effieicnt at transferring heat but don't freeze until wll below any temperature you'll encounter when mixed 50-50 with distilled water or you can buy pre-mix.
I'm not a fan of additives like water wetter and the such. All it does is make the antifreeze solution slippery. A couple ounces of Potassium Permagnate in sollution does the same thing for much less.