I think Senator Kerry is an excellent choice. He has a wealth of experience in foreign relations due to his lengthy service on that committee in the Senate, is well-known around the world, and has built personal relationships with many international leaders that will serve him and the President well once he takes over at State. I think that Susan Rice got a raw deal over the Benghazi attacks and was unfairly made out to be the scapegoat, but I also think Kerry is a much more solid pick for Secretary of State than Rice would have been.
He was only Secretary of State for two years (1947-1949), but George C. Marshall, in my opinion, was the greatest American diplomat of the past 100 years. Marshall, of course, developed the Marshall Plan, which helped relieve war-torn Europe and won him the 1953 Nobel Peace Prize.
By the way, outside of the State Department, General Marshall probably was one of the most qualified Americans who never served as President of the United States. Marshall was the Army Chief of Staff during World War II and what that means is that he was the guy who basically picked the Generals who won the war. Marshall was a priceless asset to President Roosevelt and President Truman during the war and after the war.
Besides General Marshall, I’d also include Charles Evans Hughes, who served as Secretary of State under President Harding and President Coolidge (and was another guy who probably should have been President himself). Also, Cordell Hull — the longest serving Secretary of State — who served throughout almost three full terms of FDR’s Administration.
Depending on your political affiliation, there are also many who have high opinions of other 20th/21st Century Secretaries of State. Quite frankly, the United States has done historically well — particularly in the last 50 years — with the person that have been put at the helm of the State Department. These names are all people who did some important things that significantly affected American policy and the world as a whole: John Foster Dulles (President Eisenhower), Dean Rusk (President Kennedy and President Johnson), Henry Kissinger (President Nixon and President Ford), George Schulz (President Reagan), James Baker (President Bush 41), and Madeline Albright (President Clinton). Colin Powell and Condoleezza Rice are tainted by the Iraq War, but Powell is a heavyweight on the world stage and Rice is a remarkable leader. Hillary Clinton is on her way to being a very important Secretary of State and might be the MVP of the Obama Administration so far.