We are in the planning stages right now. I've never been, a few coworkers have but they are hotel people. I am taking the TC and my family loves the outdoors, animals and hiking. We are thinking early...
Yellowstone is a huge park. If you stay at a single campground you will really limit how much you can see because you will constantly be backtracking. I recommend mapping a route through the park, staying at a different campground inside the park each night. Make sure you visit the Grand Tetons and spend a night in Jackson hole. Have a good time and enjoy.