We went last year on the Sunday to Thursday after Thanksgiving.
Sunday was a little crowded, though not outrageously so.
But Mon-Thurs were absolutely awesome! Walked on to POTC several times. 10 minutes for Indy, Matterhorn, and BTMRR. HMH and SM:GG were the only rides for which you'd consider fastpass, and that wasn't necessary, just nice.
OTOH, I hear that the week leading up to Thanksgiving is pretty crowded. I'd go right after T-Day again in a heartbeat.
-Bob