Fred Astaire and Vera Ellen - Courier and Ives finale
Last part from Courier and Ives number (Bell of New York (1951) movie) - if not the best, for sure most difficult and most sophisticated Astaire dance duet. One of my favorites.
Two best film dancers ever on the place together in mixture of tap, ballet, ballroom waltz and some folk elements. Both VE and FA is artistically great here and You can see great moments from both together or separately.
My favorites moments and details:
FA - 0:44 - 0:50 (much precise than VE), 0:55 - 1:00 (much precise again), 1:45 - 1:55 (great in legs)
VE - 0:20 - 0:43 (great artistry), 1:00 - 1:17 (artistically great again, this steps sequence use FA or Gene Kelly several times, but this VE execution is best I saw), or 1:45 - 1:55 (see her body undulation when she taps, it is another new dimension of tap she produce here) for example.