Turtle voices
 

Would you prefer the actors to use their natural voices or would you want them to create some kind of voice?

Usually acting requires some kind of "other" voice.

I think they should use there natural voices, The Turtles in the Nick series all have natural voices. Rob Paulsen who does Donatello, his voice sounds exactly the same when he did Raphael in the original series.

And in real life, as well. So does Jason Biggs.

Not "exactly"...there are subtle differences between them, because....acting. Seriously though both are still his natural voice, I'd bet you could tell a Raphael clip from a Donnie clip with your eyes closed.

Natural. This is the reason why I think it's a bad idea to put professional voice actors in the roles for live-action movies.

For some voice actors, lot of stuff sort of sounds inherently artificial. It's the reason why Josh Keaton makes a great Spider-Man, and Kevin Conroy makes a great Batman. It's basically their speaking voice with a slightly changed tone, not a full voice change.

Everything Nolan North said as Raph in TMNT threw me a little off because of the obvious voice he was putting on.

Having met Rob Paulsen, I have to say, it isn't quite his natural voice. Also, this video I shot of him highlights the differences between his Raphael and Donatello.

http://www.youtube.com/watch?v=9d5wY83yPNk

To answer the original post, I prefer voice actors who can actually change their voice over actors who simply use their normal voice.

Most likely the actors would have to say their lines again in a booth and for facial animation post-production. If they sound natural and fit the Turtle, that's fine.