MK and DHS. MK b/c the 2 mtns and the 'daisy' credits might be useful too if its busy. DHS b/c TSM and RnR. TSM is the most popular ride of all anywhere and FP are often out by noon so if you like to sleep in and want to ride without waiting an hour I'd use GAD there.
That is the 2 places we plan on using ours.
We ruled out AK b/c EE and KS were the onl y useful things to us and DS may not ride EE so that would be a waste plus that line moves very fast and I don't forsee it getting long on our trip. We are also early risers so will be able to grab FP early for it.
We ruled out Epcot b/c DS may not be tall enough for Test Track so it would be useless and we aren't sure if either of our kids are going to like Mission:Space, but it rarely has big lines either so I am not expecting to have to wait long. They have never been to Epcot so we just are not sure how they are going to like the park overall.