A summary of the first two posts gets it close to right... Airstreams in the '70s didn't get the deep-wrapped Panorama windows that Argosy did, but other than the Argosy Minuet line the Airstreams were the same width and used similar cabinetry systems as same-year Airstreams. I prefer the non-tambour cabinetry that Argosy kept for several years longer than Airstream did. The wooden cabinetry referred to in Airstreams ended before Argosy started. Argosy has a one-piece endcap usually made of galvanized steel (though apparently sometimes of fiberglass) where Airstreams have multi-segment end caps of aluminum. The Minuet line was narrower (as mentioned) and at least the ones I've seen had lighter-weight mostly-aluminum cabinetry and other furnishings, and some of them had plexiglass side windows.
While in fact the same brands of appliances were used between Argosy and Airstream trailers in the '70s, there were some subtle differences not yet touched on. For quite a few years, Airstreams got an in-countertop cooktop and a semi-in-wall oven where Argosy trailers had a one-piece range that's easier to work with now that you can't get parts for the unusual appliances in the Airstreams. I say the oven was semi-in-wall because the wall is about an inch thick, so the oven sticks back into a box that encroaches on cabinet or bunk space (depending on the floorplan.)
Another minor difference is that they tended to go "one size down" for the Argosy equivalent. Where the midsize Airstream was the 25' Tradewind, the equivalent Argosy was the 24-footer, the 23' Safari compared to the 22' Argosy, etc. Airstreams couldn't be had in a rear-door floorplan in that era and a few Argosy trailers were built on that plan.) The competitive-sized Argosy seems to usually have a refrigerator that's one size smaller than the Airstream.
All in all not much difference. For quite a few years it seemed that a vintage Argosy of length X in condition Y sold for noticeably less than an Airstream of length X+1' in condition Y, but I think that gap is much narrower now. I know I love my pano windows, and as thin and worn as my 41-year-old paint is, it looks nicer than flaking clearcoat. I know it would be a much bigger task to polish my Argosy than an Airstream with most of its clearcoat burned off by the sun, but all it takes to get it painted is money.