I have a public defender - should I hire a private criminal defense attorney?

You, your family member, or your friend may get lucky and get a great Public Defender. Having been a Public Defender myself and currently working part-time as a Legal Defender, I can tell you that there are some amazing and talented public defense attorneys here in Maricopa County and around Arizona. Do not immediately assume your public defender will not do a good job and fight for you and just wants you to plead out. Most indigent public defense attorneys know what they are doing. They are in court more than any private attorney. They have experience, a huge support system, and tons of resources. And they are free.
But just like cops, most of them are good, but there are a few bad ones. If you sincerely feel that you were unlucky enough to get one of the bad ones, then it is time to consider paying a private criminal defense attorney.