They have been pretty much the same princesses for the past couple of years. The one-on-one time (pictures and a little conversation) is with Cinderella at CRT and with Belle at Akershus, so that makes some difference.
In my opinion, Akershus beats CRT on price, food quality, and princess interaction. Of course, CRT is in the Castle. Location, location, location. If you can do both, I would say keep the special princess meal for your daughter's actual birthday.
Oh, and I would suggest you also make sure that both venues know (on the ADR) that you are there to celebrate your daughter's birthday. There is usually a little extra that they do for their birthday guests. No guarantees on that, but they won't know to do anything special unless you let them know that they have a birthday girl in attendance.