Definitely A ROOM WITH A VIEW. I was 15 at the time, (seeing it in the theater), and with all of the full frontal male nudity, was and is to this day, the gayest movie ever. (The movie Weekend also referenced A ROOM WITH A VIEW, and I experienced the same issue the character did when it first became available on VHS).

As for GAY, per se, best movie ever is a tie between TRICK and WEEKEND.