use roundup powermax brand.
you can use the other brands but they don't have as much salt in them so you have to mix about 1/2 an ounce more of it per gallon than you do the roundup brand.
the other brands have 41% but roundup has 48.7%.
you can use about 1 1/2 ounces per gallon of roundup brand but you have to use about 2oz per gallon of the other brands to get the same effect. you aren't really saving much money since you have to use more.
also in my experience the roundup brand seems to go longer between sprayings than the other brands.