I think the work of the astronomers like Galileo and Copernicus was extremely important, and probably has influenced our modern world on a more fundamental level than we would give them credit for. Without them, how would our worldview look now, I wonder.
Scientists like Newton and Einstein though are rightfully considered as heavyweights, who had perhaps the most fundamental insights into how the Universe behaves, given what they had available at the time.
However I would also say that Watson and Crick are to Einstein what Darwin is to Newton: pioneers whose work has been superceded, but their fundamental insight was what started the revolution.
Along the way you also have important discoveries coming from people like Neils Bohr, Maxwell, Planck, Marie Curie, Schrodinger, t'Hooft, Hawking, Jocelyn Bell, Susskind, and many others that have made major discoveries.
It's not worth ranking them though.
