Hey, not a NICU nurse but had cross trained to NICU when I worked at some of those facilities and this is what I know:
Largest NICU in the DMV hands down. I think they officially have 80 beds or so, but routinely have over 100 babies. Due to the fact that Fairfax probably delivers more of the high risk moms than anywhere else in the area, you will see lots of sick preemies, with the term babies that come down for various reason seems more like an exception. For stable babies you typically have 3 babies, for sicker it can be 2. Pay is OK, but I found it not to be as competitive as hospitals in D.C. free parking on site.
Much smaller NICU, maybe 30-40 beds. Half NICU is sick kids and half is more feeders/growers. They do however do ECMO which Fairfax does not. Great support for nurses. In the feeder/grower section it is normally 1:3, not sure about the more critical care part. Pay for parking, but is on site. Most of the new staff is required to rotate, only those with lots of tenure don't have to rotate.
Not sure how many beds they have. Nice fairly new NICU with all private rooms and not an open bay like the other two mentioned. They do ECMO. Will probably see more surgical procedures done here than the other NICU's in the area since babies will be sent here from other hospitals for surgeries. Only hospital mentioned where the nurses have a union. Excellent benefits, including great tuition reimbursement. Parking is free, but is at off site locations. NICU was considered one of the best floors in Children's with one of the highest retention rates.