I'd recommend posing the question on the Aulani forum too, lots of posters there have done a combined DL and Aulani trip.
I've done both places, but not at the same time. We came from the east coast and wanted to maximize our time in Hawaii, so we chose to spend all of our time there and did DL a few years later. I know a lot of people from the east coast prefer to stop in DL on the way home from Hawaii both to help lessen the blow of leaving Aulani, and to break up the long, excruciating flight home. Most of the flights home are red eyes, so flying to CA instead would give you more flexibility to fly at a decent hour.
I've also seen other east coasters say they like to DL first to help acclimate to the time change. Since we went from the east coast straight to Hawaii, we had to adjust to a six hour time difference and were wide awake by 4am and ready for bed by 8pm on our first couple of days there. Taking the red eye home, we stayed up once we got home and went to bed at our normal time, so there was less of an impact on the way back.
Being that you're already on the west coast, the time change, flight times and flight length is less of a consideration. I still would say that having DL to look forward to before returning home is a nice way to ease back into reality, so that would likely be my choice. But on the flipside, will you be touring Oahu or just spending time at the resort? Visiting Aulani after DL would be a nice way to relax after busy days walking in the parks. You're also already in vacation mode at that point, which I think helps to make it easier to unwind at Aulani. But that would be less of a factor if you plan to sightsee and be active in Hawaii as well.