Here's my breakdown for Kegs vs. Preserves Jars:
Preserves Jars give you a little more g per time spent, but you need to fill them about twice a week so they use up more Fruit/Vegetables
Kegs give you a little more g per individual Fruit/Veg but you're waiting a week for production, though they use fewer Fruit/Vegs
Kegs and Jars also have a few items which can only go in one (eg.: Coffee in Kegs, Roe in Jars), which makes that choice easy.
Here's what I do:
Fill all your Kegs with your best stuff (Ancient Fruit, Starfruit, maybe Pumpkin, Red Cabbage, Melon, Cauli) and use Preserves Jars for the rest. If you absolutely need g as fast as possible, maybe Jar during that time for the extra g and go back to Kegs when you're done.
One other key thing: What do you have the most resources for making? Kegs and Jars use different materials. And you get Jars pretty early and Kegs later in game so your choice is forced early on.