These are my opinions:

Michael Yarmush: I thought that Michael was the best voice actor for Arthur, but I am likely biased because he was the first voice actor for him. At the end (Seasons four and five), I thought that his voice was a bit deep for the role.

Justin Bradley: I am in the minority, but I didn't mind Justin's voice acting, although I definitely didn't think that it was better the Michael's. It doesn't sound too different from the season five voice acting, but if I watch a season 10 or so episode and then watch a season six episode, I am always shocked at how deep Justin's Arthur is, it does make Arthur sound a lot older.

Mark Rendall: Mark sounds very similar to Michael in seasons two and three in my opinion, and his redubs were decent. However, sometimes I don't like the redubs because he doesn't say some lines in the same tone, which sometimes affects the way I interpret them.

Cameron Ansell: I always though that Cameron's voice was quite a bit too high.

Dallas Jokic: Dallas' voice was OK, not as good as Mark, but just OK.

Drew Adkins: Ehh, the pitch is just a little on the high side, but his delivery of the lines is actually pretty good.

Carr Thompson: I liked Carr, I think that he should be a voice actor for Arthur in the main series.