It's the artifacts that get the most press, but in my layperson's opinion it's not the artifacts recovered that constitute the best evidence for the theory but rather archival evidence that's been discovered over the last 20 or so years.
Here are a couple of links that I personally found most compelling: http://tighar.org/Projects/Earhart/Archives/Research/Bulleti.... I posted this link to both Hacker News and r/history a few months ago under the title "What happened to Amelia Earhart: The sextant box with two serial numbers".
The second link is: http://tighar.org/Projects/Earhart/Archives/Documents/Bones_.... This page contains radio telegram transcripts from the British colonial authorities responsible for administering Nikumaroro in the early 1940s. The part about the sextant and two serial numbers is about half way down the first page.