Well, you don't exactly get to see who is voicing them but there some leaked voice clips of Sonic Free Riders:
http://www.sonicstadium.org/news/2010/11/first-recordings-of-the-new-voicecast-in-sonic-free-riders/My opinions on each (in the order they appear in (not including Sonic & Tails)) :
Amy - Sounds a bit like Minnie Mouse.
Cream - Not so high-pitched which is nice.
Vector - Oh my God, he sounds like Fat Albert.
Omochao - I can't really notice a difference. Maybe he's the same.
Knuckles - Not quite Dan Green but Travis Willingham hits it off pretty well.
Shadow - Sounds completely different. Still has that dark tone but... yeah. On a second hearing, I think he has a bit of Spanish in his voice. Maybe that's just me.
Rouge - Sounds more like a teen than before.
Wave - Not much of a difference that I can notice.
Storm - Still sounds the same.
Jet - Is it just me or does he sound like a higher pitched version of Joey Wheeler from Yu-Gi-Oh?
Anyway, what do you guys think?