Our first two historical polls produced very clear results (Tomorrow's eponymous release winning best related album of the 1960s with 95% and King Crimson's Lizard winning best related album of 1970 with 67%), but 1971, the year of my and Jon Davison's birth, was much, much closer. With 70 votes, the results were:
1) George Harrison: All Things Must Pass (w/ White): 15 (21%)
2=) David Bowie: Hunky Dory (w/ Wakeman): 13 (19%)
2=) John Lennon: Imagine (w/ White): 13 (19%)
4) Mainhorse: Mainhorse (w/ Moraz): 10 (14%)
5) The Strawbs: From the Witchwood (w/ Wakeman): 9 (13%)
6) Cat Stevens: Teaser and the Firecat (w/ Wakeman): 5 (7%)
7) Elton John: Madman Across the Water (w/ Wakeman): 3 (4%)
8) Colin Scot: Colin Scot with Friends (w/ Anderson, Wakeman): 1 (2%)
9=) Yoko Ono: Fly (w/ White): 0 (0%)
9=) Bell and Arc: Bell and Arc (w/ White): 0 (0%)
There was one 'other' vote, but with no choice specified.
The options were dominated by session work from either Rick Wakeman or Alan White, both still to join Yes at this point. White's two albums with former Beatles come first and joint second, although Wakeman's various appearances total marginally more votes (31 versus 28).