Overall, I think public defenders get a bad rap. Most public defenders are skilled and provide a great option for someone who otherwise would not be able to afford an attorney. The only thing is that they are usually lacking in time. They are frequently overworked.
In your case, you are unlikely to get any special attention for a petty theft. When you meet with them, which will likely be only once, they will tell you the basic lay of the land and your options. Most likely for something like this you will have an option to keep this off your record if you comply with the guidelines set by the court and stay out of trouble for a year.
If you decide to retain a private attorney instead, it is not a problem to switch partway through.
Public defenders are generally the best, smartest criminal defense attorneys around.
The one downside is that they are usually given far too much work to do.
So, they are smart - they will work hard for you - but they will not have the time to hold your hand through this process, or call you back as much as a private attorney.
Some public defenders are outstanding, while others are not. If you get a great pd, then you're in good shape. The problem is getting a lazy government worker. You are allowed to get private counsel at any time. However, if you get a lawyer too late and you're close to trial, you may not get a continuance to delay the case for the new lawyer to get ready.
Public defenders should give you the best options. However, you probably won't get to meet with them between the initial court date and the pretrial date. They are usually overworked. You may get a returned phone call though if you're lucky.
If this is your first offense without any type of criminal record (other than a speeding ticket, etc), then you should be able to get this case reduced. I'm assuming the merchant got the item back? There may be restitution owing. They may want you to pay for the investigation and detention. Perhaps you can get a trespass as an infraction. An infraction is like a speeding ticket. They are much better than misdemeanors. If you're convicted for petty theft, you'll have a theft conviction. Even with a future expungement, it can be used against you if you were to commit a new theft offense. The new offense would be able to be charged as a felony. Be careful about what you plead guilty to even if you can get it expunged. You have to consider future consequences about getting an occupational license, such as a nursing license.
You should consult an attorney. If you get the public defender, don't freak out. It's not the end of the world. You probably won't get personal service, but they should be able to get the job done.