I think quantum physics is more important than GR. And I'm talking about modern QM, like Heisenberg, Shrodinger, and Dirac, not Planck and Bohr, so it would definitely qualify for the last 100 years. QM wins over GR especially because GR without "dark matter" fails to explain the rotation of galaxies. (The fact that Einstein invented SR to do away with the ether makes me think he'd be ashamed of today's GR experts cooking up dark matter.) Also, without QM, where would we be technologically? Transistors are the cornerstone of modern technology. GR can't really claim to have yielded anything technological or otherwise practically useful. (I guess there are gravitational-dilation-corrected clocks on satellites... that's about it.)
Greatest discovery since 1961? Could be Bell's Theorem and Aspect's experiments. I feel like QED was already being developed by Schwinger and Feynman by 61. The development of string theory may or may not turn out to be a great discovery.
Greatest discovery in the last 25 years? that's pretty tough. 1986... Possibly the CMB and inflationary cosmology. Ed Witten's unification of string theory, possibly. And of course (if you're mathematically inclined,) the proof of the Poincare conjecture.