Stephen Stills is a great songwriter, too. He is a very inconsistent performer, as he is (or at least was) often way to f'ed up to play.
http://ilike.myspacecdn.com/play#Stephen+Stills:Change+Partners:342909:s29083912.8488433.3402787.0.2.34%2Cstd_423049d31970442fbf215bb86655c343
Crosby and Nash are both very good musicians, songwriters and vocalists. And yes, they were better with Young. Neil is also a terrific musician and he was at his best in CSNY too, IMO.