We've gone the last 4 years the 1st week of December. Have not been bothered by POP Warner, even when staying at POP - where a lot of the overflow stays (they overflow to CBR/FQ/POR as well) - though we were glad to have a top floor room overlooking the lake. The next yr we did not notice them at all. MGM does close early on the Friday night at the end of their stay, so must plan around that, but it was not bad at all. Oh, and we are adults traveling without children, so the teens would really have bothered us if they'd been all over the place!
Second week is a great idea - too close to Christmas for us.
It is definitely no longer a truly slow season, but the decorations are so pretty and it is much nicer than the practiclly no crowds and cold weather of early to late January!