SAS was the launch customer for 736. Traditionally SAS was flying MD80's/DC-9's before the 737. Braathens flies the 500's as NorthStar mentioned, but SAS colors are only 736's (and 737-700 and 800's as well).
I have flown countless 735 on United. Mostly from EWR
to the various United hubs. To be honest, I've found the MD80's in many ways more comfortable, especially the lower noise level because of the engine location.