Originally Posted by
tatfiend
What freewheel range?
The NR/SR rear derailleurs were ultra dependable but reportedly did not shift as well as the Suntour derailleurs of the era. The Suntour slant paralleogram rear derailleurs were the best shifting of the era until Shimano copied that feature and combined it with the top pivot spring feature from Simplex rear derailleurs per Frank Berto in his 1988 book on upgrading bicycles.
The freewheel range is very important, as is the tooth design. Adding a Shimano or Sachs/Maillard freewheel to an otherwise Nuovo Record bike makes a huge difference in rear shifting quality. The improvement with a SunTour freewheel is not as large.
Some tooth designs grab the chain more readily. Best are Shimano (and its copies such as modern Falcon) and Sachs. Next is SunTour, and last are Regina and Maillard/Atom.
Berto found that NR and SR derailleurs sufferred from overshift and inconsistent shifting on small and large cogs. Two designs had features that made a major step forward: the SunTour (and later Shimano AND Campagnolo copies), and the Huret DuoPar/EcoPar. The Huret had a vertical paralleogram that allowed the cage assembly to move up and down freely to position the upper guide wheel uniformly with respect to the sprocket. The results were minimal overshift, consistent shifting across a wide range of sprockets, and a very wide range of sprockets that can be accommodated. I've used them with several 34-tooth rear ends. Berto ranked the shifting of the Duo/Eco at least as high as the SunTours and Shimanos.
"Best" is a function of the needs inherent in your bike and your riding.