We were at Universal last year for Thanksgiving. We toured the parks Wednesday through Friday. We stayed on site and had express passes, so it is hard to judge wait times or how crowded it really was. We never had much of a wait for anything because we took advantage of our hour early entry for HP. This year may be more crowded due to Diagon Alley opening. I would say your best bet is to go early in the week. Try to avoid Friday, Saturday and Sunday.