We stayed in the 900 Loop in July. It was very nice. Premium sites, close to the Meadows Trading Post and the Pool.
We have also stayed in 100, 200 and 1500 (when we had a pop-up). 100 and 200 are very very close to the Settlement, which has its advantages, especially the access to the marina and boats to MK, Wilderness Lodge and the Contemporary.
On our next trip it will be back to the Premium sites (probably 900 loop). While the proximity of 100 and 200 is tough to beat, the size of the Premium sites has its advantages as well. If size was the only advantage l would pick 100 or 200. However, it is the proximity to the pool which puts 900 and its closest neighbors over the top for us.