Depending on what time of the year you are going, if it is in peak season, we have found it is better to visit a park first thing in the morning when the crowds are non existent. We have just been and did Universal and IoA twice each first thing in the morning. The lines were non existent or 5 minutes, allowing us to do the ride as many times as we wanted before moving on. Both parks were busy in the afternoon with lines about 45 minutes to longer for water rides. If you are going at a busy time I would recommend you devote two mornings to each park you can get it all done this way with the minimal waiting in lines.
