Coolant is coolant, it's not like synthetic oil vs conventional oil. As long as its green coolant it will work, there is no "best coolant" I would recommend buying 2 gallons Coolant without water. Because once you do mix with water, that leaves you with twice the amount; plenty of leftovers. If you buy 50/50 its obviously turned into a convince thing, so then the price jumps. And your actually getting less, but paying more.
Ex: 2 Gallons of Straight Antifreeze no water, Mixed with 2 gallons water gives you 4 Gallons 50/50 :^D... 2 Gallons of 50/50 Antifreeze costs more money, but you only get 2 gallons :^(. Hmmm mix the stuff with water yourself!! Nice little tip that not very many people think of.