Katharine and Audrey
New biographies are coming out on Katharine Hepburn and Audrey Hepburn. The two actresses never met and yet with the similar surnames, they'll always rub shoulders in any alphabetical listing.
I'm sure everyone has their personal favorite movies for each actress. My favorite Audrey is unsurprisingly Breakfast at Tiffany's, though How to Steal a Million is a close second. My mother would argue for Charade. She will find the DVD on sale and forget that we own it, which once resulted in her purchasing the movie approximately ten times in the course of a year and sending each one to me in a different care package at college.
As for Katharine, my favorite is The Philadelphia Story. (I recently watched High Society and growled through the whole movie as I couldn't help but hear every actor either trying to actively reject their predecessor's performance or slipping into the same tones.) The second-place slot, however, is crowded as I simply can't pick between Holiday, Bringing Up Baby, and The Lion in Winter.