If you can't afford a lawyer, you don't really have a choice. However, public defenders are often very talented lawyers -- those jobs are as hard to get as prosecutor's spots. PDs are understaffed and overworked, but for your money, they're the best thing going.
All lawyers are initially trained by going through law school and passing the bar exam. Public defenders are no different - they're licensed attorneys who just so happen to get their check from the state of Florida instead of from you. Their loyalty is to you, the defendant.
No, as in any profession, you will have some folks who are better, more passionate, more engaged, more dedicated, and frankly, smarter then others. In the world of private practice lawyers, you get to pick your lawyer, hopefully after speaking with him or her. In the public defender world, you just get one of them and not one of your choice. They all meet the minimum standard of ability, but yes, some are better than others.
Make no mistake, some public defenders are better lawyers than most private practice lawyers by a long shot. Some become judges and top private lawyers in time. Some stay in the office because they enjoy performing the service. Others? No so much. And, as in any profession, there may be a few clunkers too. But a public defender has the resources of an entire office behind them, which can include frequent training opportunities, investigators, access to experts, and, very importantly, other lawyers to confer with and try out ideas and strategies for representing you.
Many of my clients accused of crime have a horror of being assigned a public defender. I have never understood this mind set. Public defenders are lawyers just like private attorneys. The ones I know are excellent and care about their clients. If I had no money I'd be proud to be represented by a PD. Their only failing is that they have such heavy case loads that you might not receive attention on demand. If you want someone to hold your hand or to field 18 phone calls a day (yes I have clients who do that) you're not going to like your PD.