The correct answer to that question differs because it depends on when you are going, both answers can be correct depending on whats going on.
If you are coming during a holiday week, spring break season, over the holidays or summer break, when all the schools are out, then the weekend will be travel time for vacationers, so the parks tend to be less crowded on the weekends(but still very busy).
If you are coming during a non-holiday, non-spring break, non-summer time, then its just the opposite rule. Weekdays are the least crowded because of work/school and the weekends are the busiest times (saturdays being the most crowded) because all the locals and weekend vacationers are there.
Hope that helps.