We've been to Hawaii a lot (for coming from the East Coast), and when we went to Aulani last year, we rented a car* and stayed on Oahu for 10 days (split with Royal Hawaiian on points for 3 nights). We had toyed with island hopping as Kauai and The Big Island are our favorites, but ultimately what stopped me was feeling like we wouldn't have had enough time on the other island either (Maui, Kauai and Big Island were all under consideration). If it's your first visit or first in a while, I'd stay on Oahu. Generally I feel like at least a week in 1 place is a minimum - it takes so long to get there from the East Coast.
Also, as Aulani first timers, and given how many points it is (!!!!!) we wanted to use the resort for more than a place to sleep. I think we would have gone off campus one more day (for 3 out of 7) if we hadn't booked spa and other things all over the week. Also my kids were a little young to spend the amount of time at Pearl Harbor I'd want to spend, although our experience at the WWII museum last April makes me think that they are ready now.
*we rented an electric car and as DVC members parking is free and the electric car chargers are very close to the elevator. Win win.