Well it depends on what you are passionate about. Are you drawn to 1 particular area more than the other? Is this an area you have wanted to go into before? When I was in nursing school
I was only interested in kids or babies. I pretty much had no interest in adult care. I was lucky enough to be able to go straight into the NICU and have had no regrets.
There are some similarities between these areas but there are several differences as well. Here is a breakdown. Remember I have only worked NICU. I have no experience in the PICU.
1) The PICU has a very wide range of ages. Anywhere from newborn to age 18 and it isn't uncommon for some PICU's to have patients older than 18. Usually the "adults" in the PICU have a defect/disease common to children such as cystic fibrosis, congenital heart disease, etc... These kids are living much longer now and adult doctors really don't know what to do with them.
2) The PICU has a wider range of diagnoses. Depending on the type of PICU you are in you may see trauma patients, post surgery patients, and of course a wide variety of medical issues. In the PICU you will see a lot of kids with chronic illnesses that get admitted often. In the NICU you generally see the same type of diagnosis. LOTS of respiratory issues, but if you work in a large, high acuity NICU that does surgery you will see more variety.
3) The level of acuity varies between these units as well. Generally if a kid is in the PICU they are very sick and need the higher level of care. In the NICU not every baby is critically ill. Some babies are in the NICU just for a 48 hour rule out of sepsis and may just need antibiotics for 48 hours. A lot of babies are just a little premature and just need some time to grow and learn to feed. They really aren't "sick." Does that make sense? On the other hand you can have some very sick babies in the NICU. You could be taking care of a 1 pound baby on the oscillator with multiple drips. Also, those babies that don't seem "sick" can turn on you in an instant and become the sickest baby in the unit. Generally speaking though most of the babies in the NICU do pretty well.
4) There is tons of teaching in the NICU. Remember these babies haven't gone home yet so everything is new to mom and dad. Especially if they are 1st time parents. Throw in the fact that their baby is sick or premature and there is much more teaching that goes along with that. It may be as basic as teaching them how to change a diaper or it may be more complicated like teaching about the ventilator, trach care, etc.. In the PICU there will be a lot of teaching as well, but if the child has a chronic illness/disease the parents may be teaching you instead of the other way around. They know there child better than anyone else. Regardless, you will be dealing with the parents A LOT whether you are in NICU or PICU.
I would suggest that you request to shadow in both of these units so you can get a feel for what may be a better fit for you. Regardless of which unit you picked you want to make sure you get an extensive orientation. Everything will be new and different. You will probably feel like a new grad again.
You also need to consider what you can handle emotionally. I am a mom of 3 small kids so at this point in my life I don't think I could handle working in the PICU. Don't get me wrong the NICU can be very sad and heartbreaking, but I just don't think I could handle taking care of a 2 year old that was severely injured in a car accident or had a near drowning. I just think it would be too much for me.
Also you have to put your judgments aside which can be hard. Think of the child in the PICU that was abused and is now neurologically devastated or the mother that just gave birth to her 8th child at 24 weeks and has a positive drug screen and she doesn't have custody of any of her children. There can be some very heartbreaking situations in both units.
Also in the PICU you would likely encounter a lot of former NICU patients.
If you are in a Children's hospital that has a NICU and a PICU you usually are required to float between the 2 units so that would give you experience in both.
Hope that helps