I've used Advantage car rental through Discount Hawaii Car Rental in the past. We had no issues with picking up/dropping off or with the quality/cleanliness of the rental car. Their store front is just outside of the HNL airport, along the same street with the other car rental companies. I did notice that the Advantage shuttle didn't come by as frequently as the other car rental shuttles. We just hopped on to a neighboring rental car company's shuttle and walked over to the Advantage store.
I used to receive great rates for mini vans from DHCR. For our upcoming June 2-June 6 (Oahu), June 6-June 13 (Maui), 2018 Hawaii visit, I received exceptional rates on Airport Car Rental (saved $300 for our Oahu visit). I'm not sure if DHCR changed their pricing structure, but I guess it depends on the size of the rental car as well.