Thank you for your question.
Ultimately, there are a number of factors in play in a criminal case -what the prosecutor is willing to offer as far as a plea (if any), the nature of the crime and a defendant's criminal record
, the wishes of the victim, and lastly, what a judge is going to do.
Thus, it's very hard to predict whether a private attorney will have any different effect, but there are some important factors to consider when a defendant is deciding what is best.
1) If you choose a public defender, you don't get to choose who
you get. That doesn't mean the person isn't qualified -- they are a licensed lawyer after all -- but you don't know how many similar cases they've had, their experience level, their relationship with the prosecutor, etc. These are things a defendant can ask themselves of lawyers in consultation and make their own decision about when choosing their own lawyer.
2) Public defenders are swamped. If a defendant is looking for some hand-holding as they go through the criminal process, or to be able to reach their attorney easil, that's not realistically going to happen with a public defender. Most of them have caseloads that are huge, and are busy all day long. A private attorney is obviously more selective and has far less cases because they get to choose who they take on as clients, so they can invest more time in each case and with each client.
Another thing to consider is that many private criminal defense lawyers were once former prosecutors. They have an intimate knowledge of both "sides" if you will, and how the process works. And, they may, because of their experiences as prosecutors, have relatinships with other prosecutors and can possibly negotiate a better deal (though that is not a guarantee, of course, and any plea deal still requires a judge's approval).
A public defender normally will not become a prosecutor before deciding to go into private practice, so they only know one side of the coin, so to speak. It doesn't mean they are bad, or that a public defender cannot be effective - there are many excellent public defenders.However, it is worth taking into consideration these above factors when making a decision. Most private defense lawyers offer free or low cost consultations, so there is very little investment to talk to someone and get a feel for whether a private attorney or public defender is a better fit.