Haven't been to Chef Mickey's, so can't compare the two - but have to say we ate at Garden Grill last week and it was one of our favorite meals. Food was great and awesome character interaction - most of them made their way twice to our table.
I was unsure if we'd like it there - and actually, had been trying to replace that ressie with one for CM but had no luck. Glad we kept the ressie. It was a nice change of pace from the buffets, lots of food, and just felt relaxed in there. The kids loved making their cupcakes for dessert. It's a must do for our next trip!