Public defenders are not bad attorneys. In fact, a lot of criminal defense lawyers start out as public defenders, and I myself worked as a public defender for a while. However, there are a few things you might want to consider when deciding whether to hire a private attorney.
First, generally speaking, public defenders start out doing misdemeanors, then work their way up to doing felonies, then to doing more serious felonies, all the way up to trying death penalty cases. So if you are facing the death penalty, the public defender assigned to your case is likely to be an experienced attorney. However, if you are facing a misdemeanor, there is a good chance the public defender assigned to you will have limited experience.
Second, public defenders are often overworked and simply wont have the time to give special attention to your case. The other day a public defender told me that sometimes they will get as many as fifty new cases every day! As you can imagine, with that kind of volume, there is simply no way to give each case the necessary time and attention it needs to develop a successful defense.
Finally, it is much more likely that a private attorney will be able and willing to appear on your behalf in court, leaving you free to take care of your other responsibilities.
Something else you should consider is the fact that hiring a private attorney may actually save you money. Being convicted of a crime can cost you thousands of dollars in fines, fees, court ordered classes, and other costs. If you factor in the affect a conviction might have on your career, the total bill could easily end up exceeding six figures. You should also factor in the cost of taking time off of work to appear in court.