We just got back yesterday and would you believe that my 12DS favorite part was spraying water on unsuspecting riders at the Dudley Doright in IOA. Must be a boy thing.
He also loved MIB at US and of course Spiderman at IOA
My son who was 12 last year on our first trip to Universal LOVED Men in Black. He could have spent the whole week on just that one ride. He literally rode about 50 times during our 5 days and hit the 999,999 scored a couple of times! We had to drag him away every now and then to do something different. He liked Terminator, Hulk, Dr. Doom, Spiderman, and Dueling Dragons. But nothing compared to Men in Black!!! In fact, he liked it so much, we decided to decorate his room in that theme while he was away at camp
MIB first, then the coasters, then the water rides. We did MIB for 4 hours in a row. DS, now 14, is obviously insane (gets it from his mother I guess).
My DS 11 picks Hulk as his all time favorite ride and MIB as his favorite at US. He likes Fire and Ice better than MIB. I'm sure your DS will find his own favorites as well. There are plenty to choose from! Enjoy.