The crowds should be better than they are earlier in the summer, however as it is the summer it will still be pretty busy. The 14th should be less busy than the 15th, and the express pass is cheaper because of that. However, wait to purchase your express pass until you get to the park. The prices are the same online as they are in parks, and I have never seen the express pass sold out. It's always better to wait, because you will be sorely disappointed if you purchase the pass ahead of time and arrive to an empty park.