I have always thought that the worst season was the one in which Big River won, hands down. Do you all remember Grind, Quilters, and Leader of the Pack? Or Big River, for that matter. I saw Grind, Leader, and Big River and hated the three of them. Best thing about Grind: the set and Stubby Kaye. Period. Someone may have won a very undeserved award for best supporting actress because they had to give it to someone, as they eliminated the heading actor and actress categories. Ridiculously, Mary Beth Peil was nominated for supporting in the lead role of Anna Leonowens in a second run of The King and I; she should not have eligible, since the very same production had played a few years earlier; it had toured and returned to Broadway. I always assumed they were desperate to at least have that category.
The other atrociously bad season was the year Jerome Robbins' Broadway won. They could only find two other nominees and one was a revue (Black and Blue). Anyone remember Starmites? Re Robbins...,I wanted to love it, but -- just like a ballet gala that has incredible dancers performing snippets of great ballets -- a sameness sets in and it got boring for me, midway through the first act. That really was one of the biggest disappointments in my theatergoing life, and convinced me beyond the shadow of a doubt that I was sick of West Side Story, which (along with Fiddler) got the most time. Even though it was well-received, it was still the only musical that got mostly positive reviews; and the only book musical with an original score was Starmites, which ran for 7 1/2 weeks.
Then there is the year in which Fosse won best musical. IMO Fosse was the most awful 'best musical' I think i ever saw. That is not the reason that I identify this as a bad bad season, though. Its competition was Civil War, It Ain't Nothing But the Blues, and Parade, two of which ran less than 3 months, one for 9. I have not seen Parade, and I know there are a lot of people who think it is a great musical. Even if you take that as a given, it still adds up to a really crummy season IMO. With Fosse, they took great numbers from Fosse's career and encased them with a lethargic, overblown, pretentious wrapper.
Then there is the year Contact won. A fairly entertaining show, well done. But, best musical??? Since its competition was Swing (mediocre), The Dead (a mildly enjoyable evening), and The Wild Party, which has its supporters, but which a lot of people hated, that translates into really bad for me. And it came the year after Fosse won, which translates into a really dry period.
Finally, there was the year that Sunset Blvd won over Smoky Joes. I hated Smoky Joe's and Sunset Blvd was flawed; however, it at least had moments of greatness for me, and I still think it is ALW's best score. So, I will still list this below the other seasons.
If I had to pick one,I still think it would be the year Big River won.