Top Secret! was my favorite as a kid, but then I grew to appreciate Airplane! more, it's less broad in scope. But really it's like 1 and 1A. Top Secret! is definitely less well known though,
nobody I knew in college had ever seen it. I had like one of the early DVDs with no special features or anything.
(Same for Airplane! and A Shot in the Dark.)
I was discussing with a friend a few years ago about how the better comedies on TV at the time were single camera, no audience because of the factor Stoney mentions, how you can just keep going, you don't have to stop and mug for the audience unless you want to. (Like how Curb does it deliberately.)
I think another thing that really helps these movies work, and stuff like Hot Shots and Police Squad and Hot Fuzz even when references get dated is that there's no straight man in the main characters. Everyone lives in the absurd world and considers it normal. Always Sunny has aspects of that, but gets a lot of its humor when their world intersects with the real one but The Gang never understands what's abnormal.
Also, Top Secret! has the greatest credits of any movie ever made:
