GM and VW/Audi vehicles. For these applications, use DexCool because that's in accordance with factory coolant formula recommendations. Sure, the vehicle probably will be out of warranty by the time you get it and have to make a decision. But the OE recommendation is the safe way to go, and because you can easily obtain a DexCool, it's a no-brainer.
Ford and Chrysler vehicles. Here again, it's a no-brainer. Both companies have identified problems with DexCool, so use something else. G-05 is available in the aftermarket, so that's your choice for extended life on vehicles from those makers. However, if your second coolant is conventional American, that's fine. The recommended service interval is shorter, but if the coolant level is maintained and the motorist is not a high-mileage driver, it can serve beyond two years. In fact, Ford long recommended four-year intervals with conventional American coolant.
Japanese vehicles. This is a problem area, because Japanese-spec coolants have never been sold in the U.S. aftermarket and history says conventional American coolants work well in these vehicles. Toyota research indicates the new extended-life coolant contains phosphates to protect the water pump, and DexCool contains no phosphate. Honda has said it will not use a coolant with 2-EHA. So both carmakers exclude DexCool. Best solution with aftermarket coolants: Do a complete coolant exchange, and replace the Japanese OE coolant-conventional or extended-life -with conventional American or G-05.