I am probably not the best person to advise you as we have never done a Character meal, Joshua doesn't like going in restuarants.
It depends on whether you want a noisy or quiet atmosphere, or a hotel or theme park option.
The characters also vary depending on where you dine, so that could be a consideration maybe.
Chef Mickey's (noisy)
Crystal Palace at MK (noisy)
1900 Park Faire at the Grand Floridian (quiet)
Cape May at Beach Club villas (quiet)
These 4 were highly recommended to me, unfortunatley despite booking CP and Cape May we were unable to go.
You can book up to 180 days in advance by calling 001-407-939-3463
see
http://www.allearsnet.com/menu/menus.htm#bw