My best guess is that they are asking that out of all of the zombie lore that’s out there – live action tv, cartoons, movies, comic books, etc – which does the community think is the best of the best.

I think they want to learn about people’s favorite zombie stuff, and open it up to movies, books, games, songs, sculptures etc.

Something like:

What work in any medium, that is about/ includes zombies, is the best and why?

I think he means which zombie representation was the best among all media

What zombie work, across all mediums, does it best?

Some punctuation and the proper superlative makes OP’s title a bit more readable.