The main differences , in brake fluids , is their formulation to increase the boiling temperature. If you are doing a complete system flush, I'd go with the fluid with the highest rated boiling temps.
Because you don't know what is currently in the system , and you don't want to add some brand that would lower the boiling point of the existing fluid, I'd go with the highest rated ( boiling point) fluid for top up too.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.