[duaneb]

As far as I am aware (I use uber quite a bit), Uber X is only available in the suburbs. In the city, it's not available; I've only ever gotten the Uber black sedans.

EDIT: This is no longer true, apparently my statement about using uber quite a bit is also no longer true.

[thenmar]

UberX recently became available: https://www.uber.com/cities/philadelphia

I've taken several in center city! (unsurprisingly, a much better experience than CC cabs...)