We've been to WDW many many times and my 19 year olds never get tired of it......but on the other hand they constantly do the parks.
Also, we've been to HH as well and they loved it there too. The resort does offer some tours, like the dolphin encounter, fishing excursion (which are all offered through public island tour companies as well). You didn't mention what time of year you are going, but there's also the beach and beach house which are great fun. The beach for the teens, with a quick service food counter up by the pool is at least one full day in and of itself.
There's bike rentals to get around by themselves, there's a mall nearby, shopping and dining just across the from the resort (5 minute walk), pool table in the hospitality house at the resort, a pool at the resort. There's also golfing, and shopping and dining and a marina at Harbortown (need transportation, we had our car so I don't know if the resort provides transportation).
In short, either place is a great choice and teens being teens will find the things the like to do no matter where you go. Oh, there's also a really good pizza place (Guiseppi's I think) and ice cream shop close by.
have fun planning.
