As a previously PHL based US flyer, I would tell you to go ahead and try US. You will find their service to be sub-par, the planes to be sub-par, and their hub at PHL be a black hole for your time...

The pros of US are as you mentioned, more directs, and free upgrades, but it all depends on what you value. F on US is not worth much, IMHO.

Also another point AA vs US, and a major reason I stay will AA, is the value of the miles. AA miles for international travel, esp using oneworld awards is a great value. US redemption level on the other hand leave a lot to be desired....

As far as upgrades on AA, when are you requesting them? As gold on the routes you mention I would not expect much, but as a PLT as long as your requesting at purchase you should see some results. If you are waiting for an OP up, keep holding your breath, I have been op-uped a good number of times but almost exclusivly on the same weekly flight(s) and always because Y was oversold.

Basically you need to decide what you value most....