I use to take the kids on amusement park vacations. Once was almost 2 weeks of nothing but solid parks from early in the morning til late at night. I would buy a Six Flags season pass at the cheapest park around (prices vary significantly). Then with the cheap season passes - we could visit any Six Flags park for free with the exception of the outrageous parking fees. So off we would go, hitting every park we could find. Besides Six Flags, we did Cedar Point, Sea World, Holiday World, Disney, Universal, Kings Island, Kennywood...and probably a dozen others. I still have all the maps and season passes to this day.
I hate waiting in line, that's no fun. Here's some tips for a great time with a lot less hassle of crowds:
1) Get there when the park first opens...that first hour or so, the park is pretty much yours to pick rides as you please
2) Go to the back of the park first. Everyone is up front getting on those rides.
3) Mid-day: Then go to the front of the park. Now everyone else is at the back of the park or eating.
4) Stay late. The crowds really thin out.
5) Pick dates between holidays. A lot less people (even true with Universal, Disney not so much due to the international crowd). Right after Thanksgiving is a good time.
Universal Orlando is my favorite park. The rides are just jaw dropping. Not a lot of coasters tho, but the tech they use on the dark rides is seriously cutting edge.