I've been thinking about this and as usual, I've got to make it more complicated than it needs to be. Anyway, some good points have been made.
It makes sense that adding fluid or weights to the rear wheels is a good way to add rear ballast because it's out of the way and less strain in the rear wheel bearings. The advantage of weights is that they can be removed.
It also makes sense that adding weight by hooking something to the 3pt hitch is a good way because it can be removed even easier, just unhook it. But, it's more in the way sometimes.
Correct me if I'm wrong, but isn't adding weight to the rear wheels still going to strain the front axle because the pivot point is still the front axle, whereas adding weight to the 3pt hitch is going to move the pivot point to the rear axle and take more weight off the front axle?
One of the disappointing things about this for me is that I was planning to use my 30" rear scoop as a ballast when moving dirt. I was planning to fill the scoop first, then fill the FEL (5' bucket). Drive to the area I'm moving it to, then dump the FEL and then dump the rear scoop. That way I could move the dirt about half again as fast as I could with just the FEL. But, now I doubt the rear scoop full of dirt will be enough ballast for the FEL full of dirt. Which means I have to add weight to the wheels, which I really really don't want to do because of the additional cost and then the extra time and effort to take them off when I don't want them there.