Balance work and weight transfer
If you have such a specific goal (which btw way is great), then you won’t go wrong with either option. People get in trouble when they try and do “general practice” - without any plan or idea of what they want to work on. That’s when the bad habits kick in.
Machine or throw downs should be used to work on particular aspects of your game, and you have already done the hard part of identifying very specifically what you want to work on (balance). To be safe you should throw in the occasional net to see if your drill work is helping and then recalibrate accordingly.
Given that your goal is balance and weight transfer, I would avoid the temptation of selecting a high speed on the machine - makes it easier to time and think you’re balanced etc. Switch to slow speeds to truly see if you are keeping balance, maintaining shape and playing the ball as late as possible. Similarly with throw downs, you could do the really slow stuff (underarm one bounce feeds, or slow full tosses) to really test yourself.