We have done a Chef Mickey's breakfast, Tusker House lunch, & a Garden Grill dinner. Rated solely on food, I'd pick Tucker House.
At Tusker House there are a lot of food options out at the buffet. It is spread out so maybe that helps, but it seems like there's a lot to choose from. The atmosphere is relaxed once you are in & you don't feel rushed. The characters spend a decent amount of time at each table & pose for pictures. It was a lot of fun. Our experience did come with a negative side though. The outside area where you check in & wait to be seated was chaotic. The seating staff didn't seem to have a handle or good routine going with getting people into the building to eat. We waiting a hugely long time to even get called. Then you are escorted to an area where you can pose for pics with Donald. This seemed odd to us. Why isn't he inside with the rest of the characters? I understand keeping guests entertained & all but after the picture (& he won't sign autographs which was a big bummer for my DS), we were put back in a waiting line to get seated. It just didn't seem organized or have good flow.
My second choice I think would be Chef Mickey's. The buffet is average, except that there's just a ton of food all of the time, which isn't a bad thing. But for us Chef Mickey's was great for the show experience. They had the routine down-pat. You were ushered in quickly, everything was orderly, it was almost to the point where you felt like you were in an assembly line. But things ran smoothly, everyone got good character time & every 15 minutes or so there was some sort of singing & dancing with the characters. All characters signed autographs.
Lastly would be Garden Grill for me. The food was good, but it isn't a buffet, a select menu is delivered to your table instead. Therefore the selection is really limited. The atmosphere was neat. A rotating dining room provided for pretty constant entertainment as there are periods where you can see & hear the Living with the Land ride below you. In this restaurant you got tons of time with the characters though. Purely on time with the characters, this would probably be my #1 pick. I think they came around & spent time with us at least 3 times during our meal. All signed autographs.