There is a wrong answer, and that wrong answer is staying at Southwest. You'd be giving up minimal seniority at Southwest and you live in base. There's nothing to think about, go to United and don't look back. There is literally no reason not to.
People who complain about PBS don't know how to use it. The concessions for it (staffing requirements mostly) already happened at United and won't affect you at all. The flexibility it provides you is leaps and bounds over hard lines, all you have to do it learn it.