At the risk of offending the many europhiles in C&V I'd like to play the devil's advocate for a moment and disagree with that claim. If you agree that there are better modern derailleurs than the Duopar then I think it's a fair argument to make that it can't be the best vintage touring derailleur. Any mainstream modern derailleur design traces its roots directly to SunTour. The V series derailleurs had already been in constant development for a decade before the Duopar was introduced. There were several touring ready V derailleurs to choose from as well as long cage Cyclones. The dual parallelogram and 3 pivot derailleurs were all engineering marvels but they also all developed reputations as being unreliable and difficult to adjust. SunTour derailleurs were rugged, well designed, and most importantly they just worked, really well. What they weren't was expensive, and since their cheapness meant they could be spec'ed on bikes that were far from top of the line they weren't exclusive enough to capture the imaginations of snobbish cognoscenti of the time so their brilliance was often overlooked. It took other manufacturers another decade to catch up and to date no real improvements have ever been made on the basic design. The lowly SunTour bits may not have the cache of fancier stuff, but they looked good (in my opinion anyway), were light weight, and functioned just as well in the short term and typically much better in the long run than rarer stuff like the Duopar or hacks like the Record/Rally hybrids.

I'm not trying to insult your choice of derailleur by any means Dirtdrop, just making the case for the most under-appreciated components in the C&V world. You're willing to put up with the crummy operation of the Campagnolo piece when better options are and were readily available and it shows a bias. The Duopar is certainly very cool and I wouldn't kick it out of bed for eating crackers, but I would probably do a long tour on a nice reliable Vx while the Duopar sat on a display shelf at home.

I know that you have an affinity for exclusive and eccentric parts (most of us do) and I'm not trying to sway you, but... If pure whizzbangery is the only goal and fragility is a non issue then the Mountech seems more cleverly over-engineered than the Duopar. If class and exclusivity are the only parameters a long cage Jubilee blows the Campy away. If you've got to have geewhiz engineering and supreme unavailability at the same time the White Industries LMDS is a pure work of art. If consistent function, ease of use and reliability in the field (What to me defines "best") are top priority give me a Vx Gt Luxe, a long cage Cyclone GT, or if the 80s can play a *horrors* 3 pulley design.

That's my interjection of mechanical dorkery for the day, now back to regularly scheduled programming...