The silver finish on the HG37 is likely to be corrosion resistant.

As far as tooth profiles and friction shifting, I love HG if using an old style drop parallelogram derailleur, like Nuovo Record. With a long travel from upper pulley to the freewheel sprocket, HG grabs the chain earlier with less need to overshift, allowing the chain to run smooth even if the pulley isn't precisely below the sprocket. The single nicest friction shifting I've ever experience is with a Mavic 801 derailleur and 8 speed HG - there is a quite sprocket to ride in with virtually every shifter position.

I can see how this might not be optimal when using a derailleur who's upper pulley is in close contact with freewheel sprockets across their range, like an index derailleur.