My favorite counter service stops are:
MK - I just realized that my family and I have spent five days in MK in the last two years, I can't remember eating at any CS except for Cosmic Rays. We only ate at CR twice so we must have ate any the resorts. Regardless, Cosmic Rays is OK. There is something for everyone here.
Epcot - Tangierine Cafe. I loved the chicken and lamb platter. The bread that went with it was awesome. My wife loved her chicken wrap.
MGM Studios - I don't have a favorite here. Nothing stands out. Whatever you do, do NOT get the chili cheese hot dog at the Flatbread Grill. I had never had a bad chili dog in my life until I went to the Flatbread Grill. The chili tastes like someone dumped a bunch of fiber in it. It was very gritty.
Animal Kingdom - I never had Tusker House (which is now closed) and I got violently sick from (or on) Flame Tree. At any rate, I won't go back to Flame Tree. I highly recommend going to the Mara at Animal Kingdom Lodge for your CS. We stayed there our first trip so we ate at the Mara three times. Everything is great and the portions are great for the price. We will be going here for our CS on our next trip. IMHO, this is the best CS at WDW resorts.