Work best for what Dutchie?
I have 2 x 300ml and 2 x 600ml jugs.
I usually only need one 300ml jug as mostly Im only making one flat white for myself.
If I need to make a couple of the same I still only use the 300ml because I find it more accurate (a lack of practise on my part) than trying to steam twice as much milk in one go in the larger jug.
However, when entertaining and needing to do say 6 - 8 coffees or more, the 600ml jug gets a run in the interest of saving time.
Having 2 of each size *means I can use skinny milk and full cream and clean up after rather than as I go.