Clearly, there is no such thing as 'the best film' - because most of us lack sufficient knowledge to make an informed choice, so naturally, we select the films we like best, which is not the same thing.
I have always understood that the critics' favourite is Citizen Cain, which I've never seen, so can;t comment.
A huge favourite on these type of threads is always It's A Wonderful Life, which I found mawkish, badly scipted, edited and acted, and a complete waste of time.
But of course, it's a matter of taste and choice, rather than what is actually 'best'.
I fondly remember the 'Best' polls the music papers used to do in the 1970s' and the 'best' in each catagory was always the most popular, which again is not the same thing.
Take bass players - there is no way that Geezer Butler is a better bassist than Jack Bruce, and he would be the first to say it, but once Cream split, Jack slowly vanished off the lists, mever to return, and Jaco Pastorious who was a better bassist than both of them, and again they would both acknowledge that, would never feature because he was a jazz musician.
It's interesting to read people's choices, but they cannot all be right, and, by definition, there can only ever be one 'best' fim, and no-one would ever agree on what that is.
One thing I do know - it's not South Pacific!!!!!!!