Unfortunately neither one have a high likelihood of landing a job, as both are extremely high demand areas and competition is fierce. Few openings (low turnover) with lots and lots of people trying to get them. Try to keep an open mind, as most new grads who want peds or NICU wind up in the adult population and almost frantically upset over that. It is just the way things are right now.
I would think pediatric hem/onc would have more marketable skills, as NICU is a very specific specialty with a particular patient population that requires knowledge and care that doesn't really transfer to other populations. Both will have great family education potential, though the families of the oncology kids get to know the routines and their kids very very quickly. With that population, having the ability to respect what the family knows and does for themselves is crucial. They will usually know their kid and what is going on with him or her far better than you will if they have been at it for very long. You will need to see them as the experts and you as a partner to them. The newly diagnosed will be a great education and support opportunity though.
My opinion, which as a stranger on the Internet isn't worth much, is that you name pediatric hem/onc as first choice, NICU as second and adult hem/onc as third and pray you get one of them. Guaranteed at least 30-50% of your class are seeking out the same things though, so be prepared if you have to go to something you absolutely would not want. Very few people are getting their specialty of choice these days. You will be in better stead to roll with the punches if you are mentally and emotionally prepared for this likelihood.