Well....I never was a big fan of Queen,,,and I liked only some of Bowies stuff......Ziggy was 1972 and Night At The Opera came out in 1975. I was very immersed in prog rock in those days but I also did listen to classic rock, some pop, and jazz fusion then.
The first 2 Queen lps were interesting to me but then they started this 'campy' sort of theatrical vocal thing on many of their songs...just wasnt my style. I also had trouble with some of Bowies stylistic moves but still liked many of his rock things especially on Ziggy ,Hunky Dory, and Aladdin Sane.
NIght At the Opera is a well crafted lp but the individual songs (some silly things on it) dont appeal to me as much as the songs on Ziggy. TBH I'd take Hunky Dory over both lps.