Newton and Einstein are givens for anyone, I am sure. Fermi and Feynman are contemporaries, and I think Fermi once said he was in awe of Feynman's intellect and accomplishments. So it comes down to Hawking versus Maxwell, probably. To each his own taste! Hawking's field, cosmology, was much harder, I believe, than Maxwell's since the evidence is so amorphous and camouflaged. I could be talked into Maxwell, though, I think.