You can’t begin to talk about Armagnac without first addressing the obvious and inevitable question; “What is the difference between Cognac and Armagnac?”
Armagnac is the lesser-known cousin to Cognac while being much older. It is believed that Armagnac is France’s oldest brandy. Stylistically Cognac is Mozart while Armagnac is Miles Davis. I would love to make a contemporary musical analogy but I’m not capable.
The primary flavor difference is derived from the fact that Armagnac (traditionally) is single distilled as opposed to the double distilled technique used in Cognac. Each time you distill a spirit you refine it and make it softer but some of those rougher edges carry unique flavors and aromas.
Armagnac uses a variety of grapes; Bacco, Folle Blanche, Ugni Blanc, and Colombard while Cognac relies almost entirely on Ugni Blanc. The soils and climate differ, as Armagnac is sandy and warm while Cognac is chalky and cooler.
Many subtler, and not so subtle differences remain. I recommend keeping both Cognac and Armagnac in your drink cabinet. You wouldn’t choose between Scotch or Irish you would reach for both. When you desire a subtle, delicate brandy reach for Cognac; when you desire a robust, assertive, decadent style reach for Armagnac.