The list's title is pretty self-explanatory but I'd just thought I'd mention what was on my mind when making it was an emphasis on Katharine Hepburn's best performances. Since there are very few films she was ever in that are not at least good (from there to superb) script, direction, cinematography, rest of the cast count for much so "Best Films" seemed better than "Best KH Performances in Film". Feel free to add many films I have not.
http://www.ranker.com/list/best-katharine-hepburn-films/jos_valente,
Suddenly, Last Summer
Long Day's Journey into Night
Alice Adams
Bringing up Baby
Holiday
State of the Union
Sylvia Scarlett
The African Queen
The Lion in Winter
The Philadelphia Story