As Dennis already suggested, most criminal law work will involve presenting legal arguments in the courtroom and dealing with your local court rules and procedures, so if you decide that criminal law is where you want to go, be sure to get as much exposure to criminal law & procedure courses and moot court, and seek out internship/externship opportunities within your local court system.
Hope this helps, and good luck on your journey!
This is not an either/or decision! Many new lawyers work in the prosecutors office. Some stay there, some leave. Some become defense attorneys. For a future defense attorney, this early experience gives you insight into how the prosecutor's office works - such as how they handle their plea bargains.
As a police officer, after retiring, I worked for criminal defense and Civil Rights attorneys. My experience as a police officer helped me tremendously.
I'll let someone else weigh in on the pro's and con's, as I've never been an attorney.
If you would like to get a more realistic sense of the offices, you may be able to volunteer at a prosecutor or public defender's office. Some cities have volunteer programs. And some schools offer clinics that partner with prosecutor/defender offices. Many schools offer mock trials to help suss out what side you may be interested in.