Your preceptorship placement will not "make or break you." There are many schools
that don't offer a preceptorship at all. The most valuable things this placement can teach you are: critical thinking, time management, prioritization, and give you an opportunity to gain experience with clinical skills. My preceptorship was done on an adult respiratory floor and my first job after graduation was in the PICU. Very different populations with some overlap, but the experience that I gained managing a 4-5 patient assignment during my capstone was what benefitted me most as a new grad. The clinical skills I learned, such as tracheostomy cleaning and suctioning, chest tube care and physical assessment were also helpful.
Choose an area that will maximize your ability to provide as much care and gain as much experience as possible. Remember, there is no guarantee you will get a job in your desired specialty right after graduation. Your preceptorship should prepare you for any job, not just one. I would not choose L&D. The patient population is very limited and your ability to perform nursing skills will be limited as well. Many L&D patients elect not to have students involved in their care. If the NICU placement will allow you to perform skills, then that may be a good option. However, many NICUs allow students to perform very few tasks. If your role will be primarily observing, then this placement will not benefit you over all. You can't go wrong with an inpatient floor, and the skills you learn will be applicable no matter what area you land a job.