Next best place to preceptorship if I want to be a NICU nurse?

You have a choice? Wow, with our school we had to take what we got. Eventhough we submitted our preferences, only a couple of people got anything even close to their choices. Sorry I can't help give you feedback on your original question, however. Personally, I would go for ICU. It would help you get used to vents, etc. and making decisions quickly.

Since adult ICU is completely different from NICU, I think I would choose OB to at least get comfortable assessing neonates and initiating NRP following deliveries. You will also gain skills in breastfeeding, giving routine newborn meds, and watching the NICU team work during high-risk deliveries.

I would say OB since you would still get to work with the babies right after they're born, and learn some of the OB risk factors/conditions that lead to neonates being sent to the NICU.

Pediatric would be the best because it is the most similar to what you want which is NICU. Adults are very different and a big part of Pediatric and NICU nursing is working with the family/caregiver. This is not the same as dealing with the family of an adult patient and is a very important skill to learn to work in your desired field. OB would be my second choice. Wherever you go make sure that you get a good relationship with your preceptor because she/he can be a big help when it comes to getting a job.

I'd recommend OB. Pedi and the rest will do nothing to prepare you as a Nicu nurse. While both pedi and Nicu deal with kids, neonates are unique and nothing like pedi kids.

My vote would also be for OB for previous reasons listed.