I think Haley Joel Osment and David Gallagher both do impressive voice acting, and they really go out of their way to put emotion in Sora and Riku's dialogue. However, like everyone else on this thread, I have to say that I especially loved David's performance because of the way he did both Riku AND Riku Replica, and somehow, he managed to make them sound different, but the same. I mean, you knew it was a Riku clone in Reverse/Rebirth, so it sounded like Riku, and yet at the same time you knew he was a different character with a different personality and such. His tone, style, everything was different, even though it was Riku's voice. I don't know how David pulled it off to that extent, but he did it and I was really impressed.