I didn't mention noir qualities as such. Some noirs break into a "top" or "better" region by virtue simply of being movies that are done better, not necessarily better along noir lines but better along movie lines. One criterion is that the movie makes a deep impression, or is memorable for various reasons. The movie may be influential or handle its subplots in sophisticated ways or strike broad chords or innovate. It may fall into lower regions by its failings. How can a top 25 or X be named without getting into serious film criticism? Perhaps that can be avoided simply by asking "Is this a great movie?" If so, what makes it great?
I would suggest that if any of us proposes that a movie should be in the top 25, then we explain why it's GREAT and nothing less than GREAT. If "Pickup on South Street" is great or not, why or why not?
Take "Sunset Boulevard". It may transpire that this meets a minimum or even above minimum noir standard without those noir qualities making it great or making it stand out. This movie is great because it has great acting, writing, scenes, and echoes of real and fictional Hollywood. Everyone will remember Gloria Swanson on the staircase or riding in the car with William Holden telling him about his clothes and turning him into a kept man. Everyone will remember von Stroheim's comments about her and his relationship with her. No one will forget Swanson shooting Holden or his image in the pool. This is a GREAT movie. Perhaps its greatness as a movie, as a well-told and impressive story, cannot be separated from the fact that the noir qualities suffuse all the proceedings.
Now, consider "A Face in the Crowd", "Sweet Smell of Success" and "All the King's Men" as potential rivals to "Sunset Boulevard". And add in three more of similar nature: "The Big Knife", "The Harder They Fall" and "The Pawnbroker". What qualifies or disqualifies them for attaining a position in a top X region? It becomes critical to decide whether we are talking about 25 or 50 or 100 films and whether or not we are talking American or international productions. I think a restriction to American films is called for because not enough people have seen the many international films enough times.