To show just another way to quantify the unquantifiable title of "Best Picture", I compiled the highest rated film of each year, according to the average Letterboxd ratings. Currently only goes back to 1913 because data prior to that starts to get pretty hazy.
This is obviously a messy thing to assess, so I had to have some criteria:
1. The film must be a <film> (ie no TV shows, miniseries, stage plays, concerts, etc.)
2. Documentaries are excluded - the focus is on narrative fiction here.
3. It must be 40 minutes or longer.
4. To avoid any other weird outliers that may not be truly representative, each movie must have at least 1,000 views.
None of this is necessarily my own personal opinion, nor should it be taken as such. I'm trying to put boundaries around something very messy, so I may change the criteria if it feels appropriate to do so.