We did both on our recent trip. I preferred 1900 Park Fare which we did for dinner. The food was so much better and I liked the buffet option as we could get what we wanted and my daughter could have some healthier choices. The characters were great fun and we had a good interaction with all of them. Also, Prince Charming and Cinderella danced which was fun. Finally, I felt much less rushed and able to sit back and enjoy the meal.
CRT was also fun - my daughter has great memories of eating in the castle. We did breakfast there though and my negative comments are:
(1) Service extremely rushed - our server was trying to get orders from me as I was juggling with getting my daughter seated, my son's clip-on chair attached to the table and him in it. My husband dashed off to use the washroom and my hands were full. She was very annoyed when I asked her to give me a minute and come back.
(2) Princess interactions were more rushed than at 1900 Park Fare. Also, a few princesses put up big attitude when I asked them to move so that the light coming through the windows didn't completely ruin my photos
(3) Food was absolutely awful. I ate fruit and pastries as did my hubbie. I had the more traditional breakfast option and it was inedible. My husband had the french toast type meal and it was also bad. My daughter's food seemed okay for her.
(4) The photo with Cinderella before you go up was also very rushed and not a good interaction at all. I don't think Cinderella even spoke to my daughter. I felt like it was an assembly line over an experience.
However, it is the CASTLE and you get to see more princesses which my daughter certainly preferred to all of the secondary characters from Cinderella that you see at 1900 PF. Also, photo of my daughter in front of the castle without anyone else in it (early ADR) is priceless.
Also worth noting is that the food at CRT at dinner might me better than it was at breakfast.
Wow - that is a LONG post. Sorry. Must be feeling wordy tonight.
ETA: Back to the original question in your post (duh?). If you have the means, I'd do both on a 10 day trip. If she is princess-crazy, I'd do CRT. If she is just generally into princesses and you are looking for a nicer, relaxing meal, I'd do 1900 PF. Also, I think a boy might like 1900 PF more as the stepmother and the step-sisters are quite entertaining and would probably include him in the fun.