There could be an author named Jane Doe (assuming) who writes a lot of detailed Alvin and Eleanor fanfic. Her works might stand out because she pays great attention to the small details in their relationship. For example, she might describe how Alvin looks at Eleanor when she's talking, which adds depth to the story.
Some authors who are really into the world of Alvin and Eleanor might be the best. Those who write fanfic that not only focuses on the relationship between the two characters but also on the world they live in. So an author who creates a rich background for Alvin and Eleanor in their fanfic, like the one who wrote 'Alvin and Eleanor: A New Beginning'.
I'm not sure about the absolute best, but some authors who might be good are those who really capture the essence of Alvin and Eleanor's relationship. Maybe the author of 'The Adventures of Alvin and Eleanor' that I mentioned earlier. They seem to have a good understanding of how to make their interactions interesting.