Zerex (Valvoline) Original Green - The best Ethylene Glycol toxic-as-hell coolant still available and American made. NAPA carries it, as does Wally World, Amazon. Formula has changed recently to meet Federal guidelines for drain interval, but I still would cut the recommend change mileage in half, or more. Red is better if you have an Aluminum Radiator as its Chemistry is less conducive to Galvanic corrosion.
Always use the 50/50 if you don't have access to DI Water. Filtered Water is NOT Demineralized.