I haven't stayed at the two sites mentioned, nor the KOA.
We went there April 2012 and stayed at Cove Mountain Resort RV Park (
http://www.covemountainrvresort.com/ ). We had some amazing views greeting us each morning right outside our door, and the sites we had were spaced really far apart. The campground is something like 10 miles west of Pigeon Forge and more or less in the middle between Pigeon Forge and the mountain attractions like Cade's Cove. Since we were there in April, the pool was closed and we didn't go check it out, so I can't comment on it. The staff was pleasant to work with.
We had a friend with a 35' TT and towing with an Excusion, so their entire rig was easily 50'. Ours was right around 40' overall and our other friend was slightly less than 40' overall. I recall the sites being downright huge and easy to get into and out of.
We were in site #25, our friends with the 35' TT were in #23 and our other friends were in #46. The only issue with those sites is that they're in a field, so there's no virtually no shade. #23 had a little. In April the sun was nice (we had very warm weather for April with upper 70's the week we were there), but it could be an issue in the summer. They do have some shady sites further up the hill, into the loop.