Everything on the topic is a matter of opinion...of preference.
If you're a 'Spider-Man' fan, chances are you're gonna side with your guy.
The way I see it, you have to look at the individual film under a series of lights.
You have to look at the achievements of that film in terms of pushing the genre forward. You have to look at it in terms of the technical and financial limitations at the time of their production. Just how open were Studios to the idea of taking these larger-than-life characters seriously and bringing them into the world of live action flesh?
Were the audiences ready to embrace a figure primarily regarded as the stuff of childish novelty and juvenile literature?
You have to look at every single aspect of the production and just how in sync every department was to not only tell the story of these mythic heroes and deadly adversaries...but tell it with just the right balance of both bold reality and childish fantasy...of adult maturity and complexity with the right dash of comic book angst and tongue in cheek.
How well does the film present these characters as, what Frank Miller called them, the 'flamboyant fantasies' they are...while at the same time keeping their alter egos so grounded in depth and humanity that the audience can relate to them, sympathize with them and ultimately cheer for them.
Bearing all this in mind...
Dick Donner's film did more for this genre than any of its kind...and the facts that it was the first of its kind in 1978, had the pressure of both fan expectation and general skepticism...and eventually achieved 13 weeks at number one while simlutaneously becoming one of Warners biggest Box Office draws of the entire decade say volumes of the impact that film made not just on the concept of bringing a comic book character to the big screen...but on the entire film industry as a whole.
That's why, at least in my opinion, "Superman: The Movie" is the Greatest Comic Book Film...
I say "Greatest" because "Best" will always be arguable.
CFE