1a.Of the main cast, who had your favorite voice?
Probably Balthier, he's got quite a charming voice.
1b. Least favorite of the main cast?
Probably Fran, they butchered her voice so bad it hurts.

2a. Of the side characters and antagonists, who had your favorite voice?
Gabranth (however you spell his name)
2b. Least favorite?
I can't really say, maybe the old man who always chokes and coughs?