In the second half of the latest awards season podcast, Daniel Joyaux from Vanity Fair makes a case for Dunkirk to win Best Picture at the Academy Awards. He explains how the preferential vote works, particularly in regards to this year, as we have no clear frontrunner and the support is more widespread across the nominations. In such a case, the winner is more likely to reach the 50% threshold that is needed to win by gaining the number 2, 3, 4 and 5 votes from the ballots that favoured the first nominees to be eliminated in the count. With that in mind, he thinks that Dunkirk will have the best chance of getting those middle votes because of the assumption that most of the voters have seen it and will appreciate it, and it's less likely to receive votes on the lower end of the ranking. He adds that The Shape of Water is Dunkirk's biggest competitor, but that as a genre film it will have less of a consensus appeal.
I highly recommend listening to the podcast, it does a good job of explaining how the vote could work in Dunkirk's favour and it's actually pretty damn convincing.