Then there is the debate over using water vs. 50/50 coolant/water:

http://www.jcna.com/library/tech/tech0011.html

In Phoenix, I will never have the problem of freezing. So, in my case, DI water + surfactant is probably the choice of coolant. Why? Because DI water has the highest specific heat and won't contribute to corrosion (that water contains ions is what makes it corrosive--DI water doesn't contain ions), the surfactant will lubricate the water pump. The drawback is that water actually has a lower bp than coolant. However, as long as my system doesn't leak, boil over shouldn't be a problem (and I think I proved this by driving the car on the 106 degree day).