There are really pros and cons to both. Yes, there is more variety of food at CM and you get to see the Fab Five, however, I found, when traveling alone with DS was he was younger, buffets were REALLY hard to navigate. You would be, basically, balancing two plates of food while trying to keep an eye on your granddaughter. And, if you want seconds, you both have to go back up to the buffet. All while trying to time it so you don't miss the characters as they come by. I always found it very stressful!
GG doesn't have as much of a variety and when DS was younger I recall a trip where he only ate a roll and salad there, but it was nice to just be able to sit and have our food brought to us. The characters have always been fun there as well.