Early on, Florence Ballard, Mary Wilson, and Diana Ross shared lead-vocal duties on their recordings.  Berry Gordy though was always impressed mainly with Diana Ross; from Wikipedia:  “In Berry Gordy’s autobiography, To Be Loved, Gordy recalled he was heading to a business meeting when he heard Ross singing ‘There Goes My Baby’ and Ross’ voice ‘stopped me in my tracks’.” 

(April 2015/1)