Denny Rehberg for me. Racicot was a good Governor. Schweitzer is one of the few Democrats I would consider voting for if he were to be there nominee at some point in the future. Mansfield was one of the most important Senators in the 1960's and early 70's, and I find nothing disagreeable about him.
Rehberg is someone I have never heard anything or read anything about. Except, a friend of mine shared a plane with him on the way to D.C. My friend is even more to the left than I am and said Rehberg was just as nice as can be. They talked politics, argued and didn't agree on a bloody thing. But he was favorably impressed with him...he listened as much as he talked. That's rare today, and not just among politicians.