I think it is a matter of personal preference.

I personally prefer the wide bodies, but I have found that the AC 767's seem to have horrendous reliability (they have been flying around since the Canadian Airline era!). The AVOD is of course better on AC.

In the event of irregular operations, I think UA would handle it better, simply since they have more aircraft going to Hawaii than AC does. If the plane went mechanical on AC, you're likely stuck.

UA does charge for bags, so unless you're Star Gold, AC is likely your better choice.