I don't work for either, so here is an unbiased opinion.... Piedmont hands down! You will upgrade faster and if another app is never submitted, you will have a seat at American. Endeavor, you will be under the umbrella of Delta without anything close to a flow. The guaranteed interview with delta is a joke and everybody in the industry knows it. Delta had the chance to offer a better pipeline and were too short sided to initiate it. I guess they don't know much about the interwebz and that people talk.
Good luck my friend.