1970s and not 1970's is more widely used I believe.
Although technically 1970's is correct.
How can we possibly put Ginny Wade and Borg under the same poll?
I wont vote but will give separate opinions for Men's and Women's.
Has to be Borg in the Men's. Grand Slam titles both on clay and grass show both his quality and variation.
And it depends what you want in Women's, the best player who played in the 70s at some point of their career or the best player during the 70s.
I will go for Margaret Smith-Court in the first and Billie Jean King in the second category.