I use Prestone universal yellow mixed with distilled water, not cause I'm cheap, only cause it's conveniently available everywhere.
Using distilled water is more important than the type of coolant... using tap water will leave nasty mineral deposits inside the engine that'll block up the radiator and heater core.
Also, changing it often enough is another big thing. No matter what kind of coolant it is, it all gets acidic after a while and picks up an electrical charge... turning your cooling system into a giant corrosive hot tank. I've seen cars with neglected coolant (unchanged for 7+ years) or missing ground straps (which will ruin good coolant very quickly by forcing it to conduct electricity, which charges it up like battery acid) corrode holes in their engine blocks and eat the steel rotor off the water pump from electrolysis. You can actually test your engine ground straps and the condition of your coolant by testing your coolant voltage with a volt meter.... since I'm getting off topic and starting to feel like a high school auto shop teacher I'll let you google it if you want to know more about that.
