Hi Lisa!
Our family did both in December (our daughter is 6). Comparing the two, I think overall we liked the Princess Storybook Dining at Akershus experience better. The food was much better (my daughter liked their grilled chicken breast and cheese ravioli) and they spaced out bringing the princesses a few at a time, instead of a mad rush. The servers were quick and very helpful throughout. The princesses we saw were Cinderella, Ariel, Belle, and Alice from Alice in Wonderland.
Cinderella's Happily Ever After at 1900 Park Fare was just OK. The setting, at the Grand Floridian, is beautiful, but the food was only so-so (the food is variety from different countries). The server was nice, but I think overwhelmed (disappeared for long periods of time). The characters are Cinderella with Prince Charming, the evil stepmother, and the two stepsisters. It was cool seeing Cinderella and Prince Charming together, and watching them dance together in the middle of the restaurant. The evil stepmother and step sisters are funny, but after awhile their antics may slightly annoy (they spend most of the time walking around poking fun at Cinderella, then some of the guests). They also have these enormous dresses which will "catch" you a few times as they walk past. It's sort of dinner theater, but not on the par as, say, Hoop Dee Doo, which is terrific by the way.
So coming out I think we enjoyed our time at Akershus more. If you're looking for sort of a show experience, and put less emphasis on the food, I'd try the Park Fare. If you want a good meal, see the characters, but not all the extra stuff, I'd go with Akershus.
Good luck on your Disney planning!