I would say the main voice cast consists of Billy, Katey, and John. It’s been so long since I’ve heard John speak with his regular voice, I had to go find some YouTube videos to see that yes - I was absolutely incorrect in that regard.
Maurice and Phill are some of the all time greats and I would put them up close to Billy and Dan Castellaneta. Tress is the female equivalent of Billy, imo.
No shade was intended to the rest of the supporting cast. I feel it’s a little messed up to low key call someone a racist based on their feelings for the cast performances on a cartoon, but you do you.