Between the two I’d say Balmoral is far less expensive, if not quicker; however the best way to grind it would probably be via Railway meetings. At minimum you get one a week at the cost of raising Banditry in the Upper River, but if I’m reading the wiki right it’s possible to have both her and Sinning Jenny on the same time. Doing the Widow’s unique meeting only adds one point of Corporate Debt and 21 points of Banditry; doing Sinning Jenny’s meeting adds four points of Corporate Debt but should wipe out Banditry entirely, and also reduces Scandal by a good bit. You should be able to do both meetings twice per convention of the Railway Board, which gives you two bottle of Airag.
The biggest problem is that it requires you to have five members on your board instead of four, and it’ll take a while to get through four meetings if you don’t have Cornelius or Furnace- and even then, they might object to either proposition and require additional convincing. But if I’m right that’s two bottles of Airag a week, which is pretty nice.
The only other problem is dealing with the resulting Corporate Debt, but the Tentacled Entrepreneur or the Amused Lordship should probably wipe it out if you bring them on; the only problem with that route is you have to spend a meeting firing them next week, but it’s probably better than selling pies or tea to slowly reduce it over time.
Or at least, I think that’s how it goes- I’m not sure if it’s been updated to prevent that because it was too good, or anything.