The last time I did a nonstop between Hawaii and DEN on United, I was miserably uncomfortable. I would much rather do a layover on the west coast to get out and stretch my legs and move around.
American and United are good choices from ORD, and right now AA has some good offers on credit cards for miles. One should wait for a United cc offer of 50K or better before applying for that card, I've seen offers of up to 70K on it.
Southwest is going to start flying to Hawaii too - more details on that are supposed to be released this month. And you can qualify for a companion pass on SW which means someone can fly with you for the $5.60 in fees each direction, good for up to two years. I don't know how much fares will be, but I expect them to be competitive. Southwest flies out of Midway instead of ORD in your area. The schedule is supposed to be released on 8/30 for the period thru 4/5/2019. Southwest released a new credit card offer recently and it looks intriguing...though if you want to get a companion pass on Southwest you would want to wait til Q4 to apply for the card ( and not complete the spend requirements until 2019) in order to get the most usage out of a companion pass. That's because you can get the CP when you earn 110,000 qualifying points in a calendar year -- you'd want the points to post at the beginning of 2019 so that you have the rest of the year to earn the other qualifying points (which could be done with a SW business credit card signup bonus).
I'm a huge fan of Southwest's point system, if there's a seat available, you can buy it with points if you have enough. It doesn't depend on if there are award seats available like capacity controlled awards with American and United. If you cancel or change on Southwest, those points go back into your account and there's no penalty fee associated with canceling or changing. And two free checked bags.
As mentioned before, the Chase Ultimate Rewards system is great too, and those points are transferrable to United and Southwest. But they don't work to get you a companion pass.
If you have further interest, we are helpful over in the I Love Credit Cards thread.