And I think the answer to my question is The Godfather, I honestly don't think I've seen someone who truly 'dislikes' the film, and even those who don't love it seem to still appreciate it which can not be said for some films.
yes and I think that Godfather has pretty much everything that a good movie should have.Great source material,script,direction,music,acting,cinematography,story,characters.It also has accessibility because both movie "gourmets" and random people who don't watch many films enjoy The Godfather(that's something what,for example,Kubrick doesn't have).Even young people(15-19) like Godfather yet I'm sure they'd be bored with Kurosawa(I know that this forum likes both but in the real world Kurosawa is not as exposed as The Godfather).Finally,I think that every aspect of the film is above average.I mean,does the film has any flaws?
On the other hand,of course there can't be a single greatest film as there are many great movies and many various tastes.
Oh and by the way,I've read somewhere that if you would compile the top lists of critics and other sources which asses movies "obejctively" Citizen Kane would be the greatest American film.