Flew to Hawaii twice last year, once with UA on the Polaris equipped 777 via DEN to OGG (no connection in HNL). Came back from LIH to DEN on a 757-200 with Lie-flats. And flew once in D1 on the 767-300 via MSP to HNL (and onward to LIH) and then back via SLC on the 767-300 as well.

I was very happy with the UA Polaris seat (1-2-1 config) and would happily take it again. The 757-200 seat was also okay though no direct aisle access for everyone due to the 2-2 layout. One concern though is that UA also runs the 2-4-2 F layout birds to Hawaii and I would avoid any routing where there could be a swap to these birds. I didn't have to worry about it at the time because these aircraft were still grounded.

DL via MSP was the 767-300 and the dissatisfaction with the 767-300 seat in D1 is well discussed in this forum. It was still okay for a daytime flight but the seat is not the best or most comfortable for sleeping in and I didn't sleep well on the HNL-SLC redeye.

If it does matter to you, the DL long-hauls to Hawaii are marketed as D1 and come with lounge access. UA's product is not marketed as Polaris and does not come with lounge access. If you have access to lounges other ways this is a non-issue (or if you don't care about lounge access).

I've also previously done AA via DFW to/from HNL and at least at certain times of the year do DFW-KOA, seeing that KOA is your final. It's also not a bad choice if you can get a 777 or 787 on AA in J.