I thought I remember hearing a while back that Monday's can actually be quite crowded. I always thought Thursday was a pretty good day to go with smaller crowds.
I don't really know either but I was thinking maybe Monday would be less crowded since thursday is closer to friday and lots of people seem to take fridays off, it seems like, if they're going somewhere for the weekend and if you're going to take friday off, you might as well leave on thrusday, right?
Oh, but also I just realized that Thursday is a MM day which means if you don't have access to MM then you'll have all those people ahead of you for some of the rides. On monday, everyone has the same opportunity to get to the rides first.