Hawaiian and Aloha are very similar, but I prefer Hawaiian. The DC-9 seats seem a bit wider than the 737's, and they have more leg room (although Aloha has supposedly reconfigured so that they have more legroom than they used to, I haven't flown them since this change was made). Flights are very short, and I suspect the fasten seat belt sign is rarely turned off in flight. I often fly HNL-ITO, the longest route with service (LIH-ITO would be longer but neither airline flies it nonstop) and I can't recall the fasten seat belt sign ever being turned off. Of course, that doesn't stop passengers from getting up anyway.
Hawaiian serves tropical juice, with beer and wine available for purchase. From what I remember, Aloha serves Coke and Diet Coke, though I've been told they have juice as well. Both serve coffee on morning flights. Hawaiian has additional snacks for first class passengers, not sure about Aloha.
Hawaiian's DC-10 flights are quite good. The meal service overall is pretty good, but I have found that flight 4, the overnight "red-eye" HNL-LAX flight, tends to be a bit disappointing. On other flights I have found that the meals have been very good, especially for an airline meal. The interiors are quite nice.
If you look closely you can find a few signs of AA, the most obvious being the bare metal fuselage. On one aircraft, I could see the remains of AA's "LuxuryLiner" titles. Also, the flight attendant cabin phones have a metal plate with the AA logo on them. I assume that the new DC-10-30 from Continental wouldn't have traces of AA, but probably CO instead.
I don't hestate to recommend Hawaiian for their DC-10 and interisland flights. But if your primary frequent flier program is United Mileage Plus, that would be good enough reason to go with Aloha instead. Hawaiian participates in Continental OnePass, Northwest WorldPerks, and American AAdvantage. Both also have their own frequent flier programs.