Keep in mind that Yellowstone is a BIG park. If you stay any distance outside the park, it makes for a long drive. You really need about 4-5 days to see the park and adding a 20-30 mile round trip to that will be brutal.
Our favorite is Fishing Bridge, but you're too big for that. Grizzly is a good choice, but is at the west end and will take a lot of driving. It's located in a nice little town, which can provide some amenities.
We stayed once at Flagg Ranch. It has big sites with good separation. Lots of trees so satellite might be an issue if that is important to you. As stated, it's cool there so if you can survive on 20 amps for a few days, it's a good choice. What makes it better than the others is that it's closer to most of the big attractions, is right in between the Grand Tetons and Yellowstone and is a short trip to Jackson. If you come in the east gate, it's not far to Flagg Ranch which borders the south entrance.
There is also a nice store and restaurant at Flagg Ranch.