Water is most efficient, hands down. Coolant is an engineered material designed to prevent freezing in your engine but it doesn’t transfer heat as well. Modern coolants also prevent corrosion, especially with dissimilar metals such as those found in older cooling systems (but only if you don’t allow them to degrade). Never use higher than a 50/50 mix of coolant. I don’t try to guess any more, I use the fifty-fifty mix they sell now, even though I know I’m getting screwed.
Your cooling system is pressurized to increase the capability of the coolant to resist boiling. That works with water as well as coolant. Ultimately, the air going through the radiator is what is cooling your engine, but liquid coolant is a more effective way of getting all the remote points of your engine cooled to a safe temperature. One point to remember: You want the engine to run as hot as it safely can, since the difference in temperature between the cooling jacket is what extracts heat. If the cylinder walls get too cool, you lose a lot of the thermal energy in the cylinders. So I’m not recommending that you use water as your coolant, because the engine was designed to use anti-freeze. But when you’re not sure, water is safer.
If this is an engineering question, you will find the answer in any automotive engineering text, or in a mechanical engineering text. You don’t even have to consult a car application. Turbines, reactors, boilers, etc., all use water, not anti-freeze type mixtures, because water conducts heat better than any other fluid except liquifiied gases.