With your amount of flying you should consider whether you prefer upgrades or whether you have an SO that you would want to bring with you. If you decided to switch to Southwest, you could probably easily earn A-List Preferred and the Companion Pass, which would you bring someone with you whenever you travel. To me this is worth more than the occasional upgrade, but I'm fortunate enough to have an SO who can travel whenever/wherever. If that's not of interest to you then you're probably better off sticking with UA.