I believe right now the Japanese are the best at mixing the two, although even Ghibli made the CGI aspects of some scenes a bit too obvious (I'm specifically thinking of the rosegarden scene in Spirited Away). They usually "paint" very well over CGI, and don't overuse them.
If you want to see a magnificient traditional animated movie, try "
The King and the Mockingbird" by Paul Grimault and Jacques Prévert. It's a favorite of both Miyazaki and Takahata. The castle in the Lupin III movie "The Castle of Cagliostro" by Miyazaki was designed as a shout-out to the king's castle of that movie. Some years ago, studio Ghibli bought the rights for it in Japan, had it dubbed, and released it to theatres, just for the sake of getting this jewel known to their compatriots. I'm not even sure it wasn't a financial loss.
But reading further about it, it has been poorly distributed in English-speaking countries, apparently.