I was a public defender for 12 years and now I'm a private attorney. I was a good lawyer then and I'm a good lawyer now. My point is there are good public defenders and bad public defenders and there are good private lawyers and bad private lawyers. Your situation sounds pretty serious and you should have a lawyer you feel confident with. You should probably interview a couple lawyers and get a feel for price and ability and then see if you qualify for a PD and analyze that lawyer the same way. Good luck.
If you can afford private counsel retain private counsel, not because they are better attorneys but becuse they usually have a lighter case load and they can spend more time with the client. If you can't hire private counsel be assured that the Philadelphia Defender's association has very good attorneys working there.
Most public defenders I have witnessed in court are very good attorneys. It is a huge misconception that public defenders are not good attorneys. If anything, they may be better than a lot of private attorneys because they have more experience. However, public defenders are overworked and may not be able to give your case the attention it deserves. Your question is a difficult one to answer. If you are not comfortable with the public defender appointed to your case, then I highly recommend interviewing at least 5 defense attorneys before making your decision. Good luck!