Watching , I felt Powell had a more fluid ,languid quality while Keeler felt more staccato and foot oriented . She didn't use her upper body . It's like the comparison of Kelly and Astaire . Astaire and Powell has an ekegance in dance while Kelly and Keeler had a more athletic presentation.
I think for me the better question would be which musical do I NOT watch repeatedly ? My favorite film is THE WIZARD OF OZ. And I can honestly say I've seen it , over the course of my life so far , over 150 times. The sense of wonder, the innocence lost and refound, the friendships . And the songs, of course, keep me coming back to it . It transports me over the rainbow every time , pun intended . Haha