My husband is a teacher and has a week in April for spring break. We've gone to Disney numerous times during this week. Most times it's wonderful, BUT when it happens to fall during Easter week it's a toally different experience. This year spring break is during Easter week, so yes it will be very crowded. We;ve been when Easter was at the beginning and when it was at the end. Both very crowded times. For future info, when the vacation does NOT include Easter it is not nearly as crowded. As for if it is worse than July? We've only been once during 4th of July and would not go again. We do go during the last part of August and I can tell you that Easter week is MUCH more crowded. In the end, most people can only go certain times. Not all of us have the luxury of being able to schedule our vacations around crowds, etc. We've been at many different times of the year and have always had a great time. As long as you know ahead of time and plan accordingly you will be fine. The weather is April is wonderful.
Good Luck planning and Have a Wonderful Vacation!!