Alice Poon was great. She did some side voices too, like one of the Doom and Gloom girls.
In Roland Parliament's book he mentions he said something racist to an "Asian performer" while working on the show, and somebody here assumed it was her. Nothing has been confirmed, but it would explain her departure.
Mary Long's voice works better with older characters, IMO although I don't mind her as Molly. I think her best voice work was Rini's teacher Ms. Morino and some of the Daimon (Toden especially).