Thanks for the informative post Sixty. It is good to point out that there is a lot of value to be had in some of these old derailleurs.

When it comes to low-rent kit, I've been favorably impressed by several Suntour offerings including their Seven/GT. (Derailleurs that weigh a ton but get the job done.
One step up, Suntour's Alpha series and Bluelines are also terrific derailleurs that can be had for far less than the (now) generally recognized and well respected Cyclones and Vx's.

When it comes to Huret, I think most people who have ever owned an Allvit tend to abhor any Huret derailleur, but they don't know what they're missing. The Challenger is buttery smooth, and while the more archaic Svelto isn't quite as slick, it is (IMHO) the most beautiful derailleur ever made - even including Huret's own Jubile.

I also like the Shimano Light Action (heavy, ugly but sure-shifters) and the circa 1978 Shimano Altus-LT 'noiseless' derailleurs. I haven't found any other Shimano derailleurs that I liked, and that even includes their top-of-the-line 600 and Crane.

Finally, I don't think the much-maligned Simplex (rear) derailleurs are bad at all. (Except for their jockey wheels which break if you breathe on them - but can be replaced with durable Suntour items)
IMO, they shift pretty darn well, and I've not encountered any breakage issues in the body.
(I cannot say the same for the FRONT Prestige derailleurs, which are an unmitigated disaster.)