Grand Wailea has essentially a water park for a pool area. It's the best of the bunch for water slides by a long shot.
FS Maui has a tiny water slide at the kids' pool, but it's nothing to write home about. However, FS resorts are great with kids generally, which is why we always return. There's a game room, complimentary kids' club, good kids' options at the restaurants, etc.
Trying to status match for HH Gold, and do a 2 nighter after our 7 nights at Andaz.. Need to fill a couple nights, before heading to Oahu hitting up Disney Aulani (that is if the deal is still there for Villa come summer0).