There are non-stop alternatives to US from PHL to most major cities in the US. If you're going to Syracuse or Buffalo or Kansas City, you'll have to fly US, but otherwise you may have a choice.

Depending on how many status miles you expect to accrue and what you are going to use your miles for, US's program may be no worse than UA's. Upgrades are reportedly easier to get than they used to be on most routes.

US is better than it was a year or two ago; at least their planes are arriving on time more often. The hard product is fairly bare-bones but it's still not Ryanair.