I loved Philly- lived there for three years in my early twenties. Very affordable, great running community. I prefer west, especially 42nd to 50th, Baltimore to walnut.
Schuylkill river trail, Fairmount park, wissahickon park all nice for running
I grew up in Willow Grove @14mi. outside of Philly. My first job out of college was in the art department of the historic John Wanamaker department store. I have very fond memories of growing up and running there. My brother lives in Doylestown and I love going back there and walking down memory lane. As mentioned before, the numerous running venues are second to none.
Typical LRC, context is always key. The Market Frankford line stretches from West Philly to Center City and snakes up into the great Northeast. If you're not a local, which I suspect you're not, I'd say you're either testing your boundaries at 52nd or 56th to the west and Girard or Berks to the North. Fishtown is solid with lots of restaurants and bars. It's up and coming which means what it means. I'd say take a line on google maps from Cecil B. Moore (entering the neighborhood across to the Delaware) and under is probably your best bet in the neighborhood, but you'd be fine anywhere in my opinion especially having lived in NYC.