At Ariel's Grotto we saw Ariel, Snow White, Belle, Cinderella, Sleeping Beauty and maybe one more.
At Goofy's we saw Goofy, Max, Mad Hatter, Captain Hook, Mulan, Minnie and maybe one more.
We've also done Minnie's Breakfast and saw Minnie, Fairy Godmother, Tigger, Chip and Dale, Captain Hook and I think Pooh. I think that breakfast wasn't really worth the $.
I feel like the food is more sophisticated at Ariel's. You can order what you like. Goofy's is a buffet, and there's sure to be something you like. We liked Ariel's grotto when my daughter was at that magical age of 4 and was obsessed with princesses. She loved it. Now that she's older, I would probably go back to Goofy's Kitchen. Also, older boys would like Goofy's more.
Another tip is that we did Goofy's kitchen the day we arrived. We didn't want to waste our park tickets on a half day. This way we still had something Disney to do instead of staying in the hotel all evening.