Eyes of Nine
Everything's Fine
In terms of "greatest" I feel like there are a couple of data sets and populations that you can pull together to try to figure this out. And note, this ebbs and flows, and if you have the data set, you could potentially look at a snapshot at any given "century" (or other time frame) and try to say who is greatest. And depending on who is asking, they could lend bias towards certain data to come to an answer of who is best, for them.
- Commercial success - in book publishing; but also in other media. Many dimensions here that we could take (box office, total streams, etc).
- Peer regard - both the blurb idea posted above; but also consider things like the Nebula or Edgar awards
- The academy - this can be explicit lists by prominent 'critics' and academics; as well as juried prizes like the LeGuin awards, Pulitzer, or Booker prize
- Popular regard - as measured by popular vote awards - Hugos or Emmas in romance.
- "Zeitgeist" by doing some analytics of google searches could yield some interesting data...