When it comes to any confusion between brandy, cognac, and armagnac, just remember that the French are really specific when it comes to naming things that come from places. Let's run down a few of the terms and talk about what they mean and what you can expect from them.
Basically, "brandy" is a catch-all term that covers any spirit made by distilling wine. Most, like fine whiskies, are aged for a matter of years in an oak barrel in order to allow them to develop additional complexity. However, they're using grapes as a distillate base, not corn, rye, or barley.
The term "brandy" covers spirits produced all over the world, including American and Armenian brandies, in addition to those that aren't produced in some of the specific regions we'll talk about soon.
In general, a run of the mill "brandy" is going to be big on fruit. That might be something akin to tannic red grapes in something like the Ararat Akhtamar 10, or it could be something more along the lines of Swedish fish in the E&J XO. Brandies exist at a bewildering variety of prices and locations, with some being nearly undrinkable and others being just as good as any type of prestigious cognac.
Cognac is the "Champagne" to brandy's "sparkling wine." By that, I mean that cognac is a brandy that by law has to come from Cognac, France. Additionally, cognacs must be bottled at 40% alcohol by volume and distilled two separate times in a copper pot still. It also needs to be aged in oak barrels, but the French use a particular designation instead of the age statements more commonly found in the world of whisky.
In particular, VS (Very Superior) is the entry-level for cognac and identifies that the youngest spirit used in the blend has been aged for at least two years. VSOP (Very Superior Old Pale) is the term used for cognacs stored between four and six years. Finally, XO or Napoleon cognacs are those older than six years. However, recently the commission that controls cognac production in France decided that starting in 2016, “XO” can only be used when the cognac is at least ten years old.
In comparison to other brandies, I find cognacs to be fairly narrow in their flavor profile—which is perhaps by design. Between the grape distillate base and the French oak aging, what typically results is a spirit with a lot of candied, glazed fruit and a lovely layer of cinnamon, cloves, and other baking spices.
That said, cognac is often a hard sell for me when the bottles cost as much as the bill I expect to get from a car mechanic. As a scotch consumer, I typically expect the distiller to tell me (specifically) how old something is, and usually I expect a more natural-strength proof in the order of 46% ABV for a craft product. Cognac leaves me a little flat here, and perhaps I'm too boorish to appreciate the nuances, which is why you'll find fancy cognacs a little underrepresented here.
A weirdo category (at least for us Americans) that's beginning to gain traction among connoisseurs. Armagnac is produced in—you guessed it—the Armagnac region of France. This regional style is still a brandy, but instead of pot stills, they use column stills, distill twice as opposed to three times, and typically put the product out at a more robust strength. In other words, it's not capped at 40% ABV.
Armagnacs, based on my limited frame of reference, seem more like the brandies for die-hard bourbon and scotch drinkers. They're a little harder-edged, but typically flavor-forward. You're also supporting the little guys, which in many cases are family farmers that have been making the stuff for the better part of a century. And, because there's not a lot of name recognition here, your money seems to go a lot farther with this category if you get a wild hair up your ass and feel like throwing a random bottle into your cart.
Will you cover more?
I intend to, but I'll level with you: it's a strange category. Some armagnacs are so niche that you run into a serious problem of availability, a lot of cognacs are priced into the stratosphere, and many regular-ol' brandies are positioned as bottom-shelf fodder for the people who couldn't afford an actual cognac.
Suffice to say that if any variety of brandy shows up here, it's at a sub-$60 price point. I'm sure there are stunning cognacs in the world, but I suspect for the price many XOs run for I would have just as good (if not a better time) with four bottles of rum, two quality scotches, or three outstanding tequilas.