It's traditional to balance with the tank empty. This assumes that the tank is in front of the CG so it will be a little nose heavy (safer) when full.

For a serious aerobatic plane the nearer you can get the tank to the CG the better. That way the balance will not change as you burn off the fuel. Of course if you get the tank right on the CG it will make no difference at all whether you balance full or empty.

Steve