As far as performers go, hands down it is the Kingston Trio. Yes, they were not the most accomplished musicians; yes, they were quite apolitical (at least until John Stewart); and yes they homogenized folkmusic; but the trio made acceptable the music that enjoyed a tremendous popularity for nearly ten years, and which continues forty years later,

They led the way for PP&M, the Limeliters, etc. The more serious folkies, the Carolyn Hesters, Joan Baez, Judy Collins, Frank Proffitt all profited (pardon the pun) from the interest they sparked.

Are they my favorite group, not by a long shot...but thank heaven for them.