As they point out:
The song was written by Joni Mitchell in 1967 and was first released by Judy Collins in the same year. Joni also recorded her own version of the song in 1969. Fast forward to 2012 and we have Carly Rael Jepsen’s version which appears on her EP Curiosity which was released in Canada.
Judy’s version introduced the song to the public, but I think at this point it’s safe to say that Joni’s own version is the most well known. Carly Rael Jepsen placed third in the 2007 season of the reality TV singing contest Canadian Idol and is currently most known for her pop hit “Call Me Maybe” (which, incidentally, she originally co-wrote as a folk song).
You can vote for your favorite. Not sure how long they keep the poll open. When I last looked, Joni was in the lead.