Lots of my coworkers love WN and choose UA only if WN does not fly there. Their primary reason, is you can change at will and points accrual and redemption are easy to understand. Plus free snacks and occasionally free drinks. The checked bag fee does not matter as most do not check bags.
I stick to UA, inspite of their drawbacks, primarily for international travel and lounge access. For me UA is not any worse than AA or DL or even WN overall, with seat/plane comfort may be superior in AA/DL, but their frequent flyer programs are atrocious (especially DL) when compared with UA.