Now, I have my pet peeves. I don't like abridged audio books. I prefer professional readers to volunteer readers and big-name actors. And I won't listen to a book with a poor reader, no matter how much I like it.
That said, let me return to the point about actors/professional readers. Some of my favorite readers, including Simon Prebble, Patrick Tull, Hugh Dickson and Rosemary Leach are also actors, either on stage or in film. Some do work for radio. But they aren't big name actors, and reading is obviously a way for them to supplement their incomes.
Other actors, such as Derek Jacobi, are not readers, but they get chosen to do readings because they are well-known. That is, Derek Jacobi, who played Brother Cadfael in the movies, reads Brother Cadfael books and David Suchet reads Agatha Christie Poirot mysteries. And they are terrible. David Suchet, who is a magnificent Poirot, is a terrible reader.
In other words, reading is a gift. On the opposite tack from David Suchet is Ian Carmichael, best known as Peter Wimsey. It is obvious even from the films that Carmichael understands the role (much better than Edward Petheridge ever did), but he just looks wrong, like if you cast David Spade as Darcy (David Spade would make a excellent Wimsey, by the way). However, as a reader, Carmichael is incomparable. He is one of the best out there.
One of the attributes I like in a reader is an ability to read different parts without taking the time to "perform." That is, I want a fast reader (Patrick Tull is a great reader but a little too slow for my liking), and I want to get a sense of the characters, but I really don't want a reader's theatre kind of deal. If I wanted that, I'd get a reader's theatre tape/CD.
On the other hand, I want some inflexion (which is what amateur readers aren't too good at). Ian Carmichael supplies all these qualities.
Here is my list of good readers:
Joan Hickson for Christie's short stories/Rosemary Leach for her long stuff
Simon Prebble (most beautiful voice)
The magnificent Tony Robinson (yes, Baldrick—he mostly does children's books)
George Guidall reading Dante's Inferno (may have to go to your library for this; it's worth it!)