I think you can overplan. You really can have a great vacation picking any of the parks to visit on any of the days.
I'm not saying there isn't a lot of good advice out there, just that your vacation won't be ruined if you pick the wrong park to visit. It might be ruined if you drive yourself crazy trying to figure this out.
If you've read everything (and it sounds like you have) and you still can't decide, here is what I would do. Head out for the busses. Whatever bus comesfirst , that's the park you go to.