It's gotta be up there with, like, writing and fire, in terms of shaping the destiny of our species.
But farming is an incredibly long series of incremental improvements since prehistoric times: agriculture, selective breeding, crop rotation, etc.
The pill was like a technological and societal step function.
2. Consistent effectiveness.
3. Able to be unilaterally adopted by women without consent of men (aside from systemic legal prohibition).
The pill, to a greater degree than any other contraceptive, enables the people who are most responsible for the consequences of pregnancy to have the most control over pregnancy.