What do you think about the importance of voice actors in movies when it's a non-human character? In my opinion, the actor can make or break the character and is capable of making you either love or hate the movie/TV show.
One example comes to mind: Smaug, the dragon in The Hobbit. I think Benedict Cumberbatch did a brilliant job there.
I am not sure if it would "make or break" the character honestly, but voice actors are important to a certain extent. Everyone's taste is different, and while you think Smaug was done well, another person might hate that voice. I think it's subjective.
My favorite voice actors were from the 40's, 50's and 60's.
Most are in this article but in my opinion June Foray, Hans Conried, Bea Benaredet, Daws Butler and Paul Frees should have been much higher on the list. But they were the voices of my favorite cartoons and that's my bias.
Mel Blanc is listed as #1 and it's hard to argue that. He'd either be at the top or very near the top of any such list.