findark, te number of options out of GRB to KOA is why we fly United. I wish there were more one stop options though. To my knowledge United runs a seasonal ORD to KOA but we generally fly mid February and that flight is not offered at that time. Our favorite flight is UAL 219 to Hawaii and UAL 218 back.
Delta was just an interesting option and the consensus is Delta, or at least Delta One is a distant second place to United and their Polaris seats.
Delta also offers GRB to MSP to SEA to KOA with a 3 hour layover in MSP and an hour+ in SEA. Only advantage to that unpalatable itinerary is a 6:15 0r arrival at KOA.