Its not a joke, just my opinion. I see public defenders and private defense lawyers every day. No one has as much court experience as a public defender; they know their courts better than anyone. Private criminal defense attorneys are hit or miss. If you are going to go with a private attorney, I'd only hire one who was a former DA or public defender with plenty of trial experience.
The private criminal defense attorneys i have seen are relatively poor. If you're a good trial lawyer in private practice you'll be making big money doing PI or suing corporations, you wont be waisting your time with defending people for little money.
If you want verification go down to your local superior court and sit there for a few hours. You'll soon realize the difference. I think the reason people don't value pd's is because the office doesn't have the resources like a private firm. For instance, a pds office wont normally get multiple experts, independent lab tests, private investigators etc. A private firm is able to acquire these resources more easily and pick at the prosecution's case. If you're case is relatively simple and rests on oral testimony, I would go with a public defender- but thats just my opinion.