Like BlackJackDelta, we usually go beginning to mid August before the lower tier AP's become unblocked. We always have a great time, there are crowds, but pretty easy to navigate with a little planning.
We went last year the week after Thanksgiving and would do that every year if our schedules allowed, which they don't.
We are thinking of a trip next Thanksgiving since we wont be going this holiday season. We know it will be crowded, but we can plan around that and still have a great time.
When we do go during the peak days, we always try to add an extra day, we know there will be crowds, get there early, grab FP's, take a break, just enjoy yourself. Holiday time in the Land is so worth it if you can swing it, even with a few extra people in the way.