the beginning of the week will be less crowded than the end of the week, and the weekend.
But since Universal doesn't 'funnel' the hotel guests into 'early entry' days at the two different parks,, it doesn't matter which one you go to on any given day. IMO IOA may be slightly more busy in the morning, because people want to be the first on the Hulk and Dueling Dragons. Others may have a better idea tho