My working field is the vocal pop and jazz. For the lessons I’m teaching, I have made a handy overview of the twenty most important vocal groups of the past century.
With this concise history you get a good image of the period in which the groups were active, how long they played an important role and what influences they might have had. (The most fun is actually not looking at such an overview, but creating it. I love making lists.)
Here it is. Needless to say that the choice of groups that made it to this top twenty is highly subjective: