I think it's a toss up between Monday and Tuesday in terms of lower crowds. Tuesday is Veteran's Day (as the PP noted). So some folks might have the day off, which could increase crowds (only SoCal Select APs are blocked on Mon/Tue). Monday might see some crowds as well if folks are thinking of making a four day weekend of Veteran's Day (I don't know if anyone gets Monday off instead of Tuesday).
Personally, I would probably opt to risk crowds and go on Sunday (9/9). Both SoCal and SoCal Select APs are blocked, but Deluxe, Premium, and Premiers are valid. Still Sunday is likely to have longer hours and more evening entertainment (fireworks, Fantasmic, WoC, etc.).