When making havdalah, is it best to stand or sit?
There are varying customs, both are acceptable. One who has no custom in his family or community should sit.
See Shulchan Aruch 296:6 where the Mechaber rules to sit while the Rama notes the widespread custom to stand. The Vilna Gaon rules like the opinion of the Mechaber to sit. See Igros Moshe O:C 5:16 who explains at length that standing for kiddush or havdala should only be done with the precedent of a minhag, barring that one should sit.