Voting methods for Primaries with Proportional delegate selection

What voting method would best fit in with current presidential primary elections, in which the result is intended to be a set of delegates for a future convention?

I found this article interesting, and it also notes that there is a recent ranked-choice YouGov poll in California of 1,507 registered California voters for Stanford University’s Hoover Institution and the Bill Lane Center for the American West, which they reanalyzed the data to reallocate votes for candidates with less than the Democrat’s 15% support threshold:

Note that I think there are yet better approaches, which might eliminate primaries entirely. But that’s a separate topic.