It's a nice question.
Off the top of my head, i guessed the A's or the Pirates. Then, i thought that the Chisox only loss in the WS was in 1919. So i didn't recall that they had won 2 earlier in the century but lost to the Dodgers in 1959.
So it has to be the Pirates. Has any team done better than 5 of 7?
This question, which i had never considered, really stumped me.