I had flown both to HNL. They're both not that great, but not as bad as people say either. The seats in NWA seems slightly better, wider and more leg room. NWA has mai tai onboard. DL doesn't. But DL's food is better (shocking, I know). DL's FA are also alot better, much friendlier. They even gave my in laws a bottle of wine as it was their anniversary. DL's award availabilitiy is also better, at least for me.

You should choose base on where you fly out, and the time that fits you the most. And if you're paying, just pick the cheaper one.