This post is totally personal and your mileage may vary, of course, but, what gigs of the magic tour you think are the most important, you can considerate all the aspects you want
Budapest by far is the most important gig of the tour, Queen went to a new audience, and for the first time EVER a band did a stadium gig in a URSS country. With a great crowd (70.000-80.000) the band make one of the best shows of the tour, with killer versions of ''Tie Your Mother Down'', ''Tear it Up''(Maybe the best rendition of the song), ''A Kind Of Magic'', ''Under Pressure'', ''Who Wants To Live Forever'' and ''We Will Rock You''. Also they did the special hungarian song and filmed the gig in 35mm. Obiously they put and extre effort here.
Second comes Knebworth, their last gig, with the band in a superform (in fight with Budapest and Leiden) and the biggest audience of the tour and one of the more enthusiastic.
Third the Wembley shows. Wembley is a very special place for the British, and is/was located in the Queen hometown, they converted this gigs in their iconic performance, also the most mediatic of the tour, i think. The band and the crowd were OK.
If Wembley is special, Slane too. With the second biggest crowd of the tour and in a beautiful place like the castle, this gig could be special for Queen career, and of course was special for Irish people, too bad the crowd were so wild
And Leiden gigs were KILLER gigs, specially the first two, the band were in great form and the audience was the most enthusiastic of the tour, i think. Also, three of the few gig in arenas of the Magic Tour, when the standard was a stadium.