About the only advantages of US over UA...

1) Upgrades are free for all elites and one companion. (Nothing beats getting four cheap tickets upgraded to First for free when I fly with my family--my wife has status too.)
2) The challenge for US is fairly attractive compared to many other challenges. (Of course a free match would beat a challenge.) You get the benefits of status (like upgrades) from the time you start the challenge, and can even hit their highest level (CP) if you fly 30k miles during the challenge.
3) Upgrade percentages are very good with US, even at lower elite levels, especially if you can avoid the typical business travel times. I hit 70-80% as Silver and have been 100% as Platinum.

Other than that, UA probably has the advantage on almost anything you look at. Weigh those three things and that should let you know if you should dig deeper.