Would you trust a public defender to handle your murder trial?:
Well, a private attorney in a murder case is going to run you between 30 and 50 thousand dollars.  So if you don't have that kind of money, you might not have a choice.

In general, public defenders are decent enough attorneys.  Their main problem is they tend to be overworked.  I mean, they are buried in work.  This gives them less time to devote to even the most important cases.