My personal experience, for what it's worth.

Front derailleurs: Campagnolo NR and SunTour Cyclone are comparable and very good, but having broken a SunTour at the mounting clamp, I give the edge to the Italians on craftsmanship and durability.

Rear deraillerus: I concur with Frank Berto regarding overshift in the Campagnolo NR, but one quickly learns how to compensate automatically.

Shifters: My ca. 1970 SunTour downtube levers, with their plastic inserts, were very difficult to tension just right for easy shifting without unintended upshifts. Campagnolo levers from the same vintage tend to require much less frequent retensioning.

Cogsets: I typically run 2-tooth progressions with an SRAM PC-58 chain. My least-favorite freewheels is my ca. 1980 Regina America 13-15-17-19-21-23. Upshifts are fast and crisp, but downshifts are occasionally slow, and I can sometimes (fortunately, rarely) skate the chain over the tops of the teeth on the 19T or 17T cog. I have an otherwise comparable standard 6-speed 14-16-18-20-23-26 SunTour Winner unit on the Bianchi, with the same chain and also with a Campagnolo parallelogram rear derailleur, and I greatly prefer the SunTour.

Chains: I use SRAM PC-58 exclusively and have a stash of spares and no plans to change.

Hubsets: A look at the cones and races of my 1960 Campagnolo NR units is enough to make anyone a believer -- Campagnolo bearing surfaces are accurately machined and extremely durable. The first owner had neglected maintenance in a way which would have damaged Normandy hubs severely, but these Campagnolo hubs have cleaned up beautifully, and the axles spin smoothly and easily with new ball bearings on the old cones and races.