so hard, they both are huge icons for a reason. I'd say Katharine is the better actress, but Audrey probably has more cultural relevance today because girls still buy the BAT posters of Audrey in her LBD and pearls, and from being on a college campus, every year a sorority dresses up in that costume for Halloween.
That being said, Katharine will always be remembered for her 4 Best Actress Oscars...no one is ever touching that record, not even Meryl. She may get a fourth Oscar, but not 4 Best Actress Oscars.