Welcome to FlyerTalk and the US forum, 747freightPilot ^

I believe the rule of thumb is to join (and achieve status in) the FF program of the airline you fly most. If you're flying US a lot, then the US Dividend Miles (DM) program is the place to be...

US DM prides itself on having the most generous upgrades of any airline. So if it's upgrades you seek, you've come to the right place!

Most FTers save their Miles for free trips; since this is not a top priority of yours, your Miles could be better used to upgrade when you book (based on availability) and not having to wait until your Preferred upgrade window opens for a complimentary upgrade.

Happy flying ...