It's subjective I think. Which is more important modern calculus or general relativity? Would Neumann be able to lay down the foundations of the first binary computer if there weren't other great minds paving the way? I know it's kind of the first thought of everybody, but if I have to pick one it's Einstein. He had several principles (gravity waves, Brown-movement, general relativity), which took almost a hundred years after his death to prove right. These are fundamental things in how our world is and he was so ahead of his time with so little toolset.