I just listened to Pit, Palutena and Medusa's japanee voices. Though they are really good, I think the English one are better (and like Oniric Spriter, I like my animes in japanese :o)
I think the english voices managed to understand the character more, and have more personality. Especially for the goddess, Palutena's voice seems more calm, yet with a cheerfull, almost troll tone, and Medusa is more aggressive, while the japanese is more of a generic "evil woman".
I still have to listen to Viridi's loli voice, though