Public defender's are just like any other lawyers. Some are excellent, some are not. Beyond that, there are advantages and disadvantages of having either. The greatest advantage to having a public defender being the cost.
I worked as a public defender for several years prior to private practice. While I think I did a great job then and still do now, I can tell you that my current clients get a much higher level of attention than I was able to give my clients as a public defender. If you can afford to hire private counsel, however, I would strongly suggest you do so. While the behind-the-scenes legal wrangling of both private attorneys and public defenders may be similar, the increased interaction you may have with private counsel will likely go a long way towards preventing you from getting ulcers, and helping you make informed decisions.
Besides, you may not even qualify for the public defender.
Some lawyers are great, some are good, some are okay, and some are not good. Whether they are public defenders or private attorneys, they could fall into any of these categories. If you hire a really cheap private lawyer, then chances are that s/he is not very good or their fees would be higher. Some public defenders finds themselves overworked. But, they are in a situation where if they have a question, they have a group of lawyers with whom they can confer.
Talk with several lawyers by telephone. Compare what they tell you to what the others tell you. Determine how you feel about them, and whether you are comfortable. Then, visit with at least two of them to talk in detail and to get fees quoted.
If you can afford a lawyer, then you probably do not qualify to get a public defender anyway. If you find that you cannot afford a lawyer, then you can apply for a public defender. Work with whatever lawyer you end up with for the best results, but do not pester the lawyer frequently - if they are chatting on the phone they cannot be working on cases. : )
There are great public defenders out there, as well as poor ones. The problem with many public defenders is the high case load that they endure. Even the most dedicated public defender often doesn't have the time to give each case the attention that it deserves.