If going with a free agent DE...I'd likely favor Jabaal Sheard.
Sheard showed a solid level of consistency as a rookie & 2nd year player at right defensive end in the 4-3. He basically averaged 55 tackles & 7.5 - 8 sacks in his first 2 seasons.
Things to like about JPP include his age, versatility, size and athleticism. But he will likely get a pretty good size contract, one that may simply be too cost prohibitive given the other players the Cowboys need to sign. I also get somewhat of a bad vibe about JPP in terms of consistent effort...particularly after getting a big payday. Then there's the back issue.
Really like Justin Houston...but he'll command BIG money, and will likely be franchised if the Chiefs again can't reach a contract with him. Love Greg Hardy's talent...but not his troubles. Jerry Hughes is interesting...but the talent around him gives some cause for pause in terms of his production. I like him though. Have seen some mention Brian Orakpo on a prove it type of deal given his injury issues.