I'd go with Universal or Sea World but they both have pros and cons. I think the 13 year old would get kind of bored with
Lego Land on repeat trips.
Sea World to me is more of a relaxing day, Mako is one of the best coasters around though. Typically if I go to Sea World it is just for a few hours. Their APs are also fairly cheap (I have the BG/SW silver pass) and there isn't a down payment with Florida res flex pay so you just pay whatever the monthly rate is to start. They often have sales though so the price varies. You can also add on Busch Gardens for not that much more money but it's just far enough that I don't make the drive very often.
Universal is going to be closer to Disney as far as level of entertainment, and the Velocicoaster is opening June 10. Main downside with Universal obviously is the cost, and if when Disney starts selling APs whether you'll regret spending the money on Universal instead (or in addition to) rather than going to Disney. I love both personally but I know my mom for example got a Universal AP a couple years ago because she lives out of state (barely over the border in GA) and the platinum Disney AP is just too expensive. She liked going to Universal but she doesn't do most thrill rides so it really just made her miss Disney more.