I've never been to Universal on Thanksgiving day but the crowds early in the week aren't too bad considering a holiday is coming up. The weekend...on the other hand...is a zoo!
I've been a few times over that period and compared to WDW the days before Tday are MUCH better! As for Tday I think is a bit better but the Friday and Sat after it's all crazy! I usually go the Monday or Tuesday before Tday.