I have a rather unique setup, which is the only reason I'm still able to do this without losing my sanity or my liver. For the past 7 years, I have been the head of a very small PD's office in rural Northeast Georgia. I have as much autonomy as someone in my position can have, and only have to answer to my clients, which is as it should be. There aren't any of the political headaches that often exist in a "big-city" PD's office (Atlanta's is notorious for that kind of thing), and I carry a full caseload, which most PD heads aren't able to do.
I had a professor who was a former PD in Oakland, CA. He said that he rarely advised his clients to go to trial because the evidence was often overwhelming – it was his experience that plea bargains were usually the better deal for his clients. He also cited a statistic that 95% of PD clients accepted a plea bargain and that 90% of those who went to trial got convicted.
This information is somewhat anecdotal, since he just mentioned it in passing and didn’t mention the source of his information. And I don’t know if he was speaking nationwide or just for Oakland. I also don’t know if the conviction rate was for the most serious charge against the accused or if it includes convictions for lesser charges.
Hopefully a PD or criminal defense attorney out there has some more info.
As an aside, this guy went to Harvard Law School, so it goes to show that you can get good PD representation. I imagine it is especially true in big cities, where idealistic young attorneys would be more likely to settle.