Oddly enough, we eat at California Grill because we feel like when we eat there we're on a
Disney Cruise. I know that may sound odd, but with the prix fixe menu and choosing the appetizer, entree and dessert that's all included, it gives that cruise vibe. Additionally, even though we've had dishes at California Grill that range from absolutely amazing to just okay, the servers there have always been exceptional, much like the servers on the Disney Cruise ships, and they're always willing to make it right if you order something that is just okay. This makes it a good place for picky eaters who may not initially like what they ordered. We've eaten there countless times (gosh we miss the brunch they used to have!) and its always a favorite!
Topolino's isn't as grand of a place as California Grill physically, but the food more than makes up for it. We've dined there 3 times and they've all been excellent! One time we ate there, our server was so amazing and after chatting with him, we learned that he was actually a server at Victoria and Alberts, but they were closed for remodeling at the time, so he was serving at Topolino's in the meantime. We've never done breakfast there (we're not character dining people), but the meals at dinnertime are constistently good.
Overall, both are solid options! California Grill has better physical atmosphere and views, but Topolino's gives picky eaters and those who maybe don't eat a lot the chance to order a smaller meal.