We consider Akershus our backup to Cinderella's Royal Table. They have the main ones cycling there. We also like the food & atmosphere, so I would deff pick that one if you asked my personal opinion.
1900 Park only has Cinderella themed or the Alice/Mad Hatter one. The other headliners like Snow White, Aurora, Ariel, Belle & Jasmine don't cycle there.
You aren't guaranteed any specific characters at Akershus or CRT but you will get main ones, sometimes they throw in backups (I suspect when people are sick or etc).
I doubt they will allow Ana & Elsa to appear at any of the current Princess dining options. It appears they are only available at the M&G in Fantasyland. I assume at some point they will create lots of Frozen things (maybe rides or dinners etc) but for now they are just too popular and would overwhelm the restaurants with mayhem.