There is a a big grey area between very good amateur and professional quality, depending on what one expects and on personnel taste. Anyway, here are some of the very best LibriVox readers:
Ruth Golding
https://librivox.org/reader/2607
Cori Samuel
https://librivox.org/reader/92
David Barnes
https://librivox.org/reader/94
Andy Minter
https://librivox.org/reader/152
Mark F. Smith
https://librivox.org/reader/204
Ralph Snelson
https://librivox.org/reader/2140
Kara Shallenberg
https://librivox.org/reader/19
On their catalog pages click on "solo" (upper left part of the page), to get only books read entirely by them.
A good way to find readers you like is to check out the many collections on LibriVox, mystery, Sci-Fi, short works, non fiction, ...