Your most important question should not be "what kind of coolant should I use?" -- it should be "why am I losing coolant?!"
Lots of people recommend something like Dexcool or other water-free coolants, citing "cavitation" issues with standard coolants, etc.
I personally use standard coolant/water mix, and have done so for the life of the truck. 150k hard miles later, no engine or cooling issuesof any kind. Plus, you can top off with water or a mix as needed, which can come in handy on the trail or road if you run into an unexpected problem...