Hi there and congrats to your friend on landing a gig at a NYC consulting firm=)
As a fellow consultant for a couple of years out of IAH, I have a strong personal bias for CO due to a 19/20 internal upgrade in a busy travel year while being a lowly Silver even when doing the dreaded monday-thu shuttles. In addition, the fares from EWR to rest of USA for personal on CO is cheap while still earning full miles with the 125/150 based on silver/gold.
For the OW, I defer to the rest of the forum.
One side note to anyone moving to NYC, SW just started flying to LGA --> cheap personal flights while consulting world = EWR or JFK hops which imply (to me) CO or DL/AA respectively!

One must do is to work the consulting forces for mileage on expense which might be more valuable than even the flight miles since hotel *5 days weekly is a fun extra bunch of points.

Enjoy the NY visits with a friend there!