Depends very much on where their base interests lie. Do they want to be an intensivist or a neurologist at heart? The length of training is essentially the same (5 years for Peds Neuro + 1 year Neurocritical Care - so 6 years vs 3 years Peds, 3 years Peds Critical Care and 1 year NCC; 7 in total), but the way in which that time is spent is very different and the skill sets one develops on each path are very divergent.
In terms of finding a job, at the moment it's probably pretty rare that any group (either PICU or Neuro) is going to let anyone do nothing by Neurocritical Care for the entirety of their clinical time. PICU groups are going to hire someone who will do regular PICU service time (and all that entails) as well, while neuro groups will still expect some sort of time in neuro clinic (though it may be a majority of NCC follow up clinic) and possibly non-ICU ward service. Both sides at academic medical centers will expect research and administrative duties. Neuro provides a built in "escape" of outpatient clinic if NCC leads to burnout that isn't quite as available in the Critical Care world (at least at the moment).
Put another way, NCC typically focuses on PICU pts with status epilepticus, encephalopathy, stroke, and TBI. Being an intensivist means you'll also develop expertise in ventilators, trauma, sepsis, ARDS, asthma, DKA, congenital heart defects and post op management. Coming from the neuro side means that you'll know far more about outpatient management of seizures, motor disorders, cerebral palsy, neuro-degenerative disorders, genetic syndromes and like. Does your friend want to be a generalist on steroids (critical care) or an uberspecialist on one organ system (neuro)? That's the question they should be asking themselves.
