I am NYC-based and will avoid JFK and Terminal 4 at all costs for a domestic flight that can be flow from Laguardia. Yes, there may be more lounge selection (Virgin, Centurion, Chase, Delta One for those with access) but I see no good reason for anyone in Manhattan or NYC for that matter to pick JFK unless they live in Eastern Queens or Brooklyn near JFK. The walks are long, operations are a mess, and I find Delta staffing overall much less helpful. Good luck if you have a baggage issue irrespective of status. Yesterday my flight arrived about 50 minutes early only to lose the 50 minutes plus a few minutes more waiting on the tarmac as the gate was occupied. And that's a regular occurrence.

Plus I landed at gate B53 which meant a walk probably double the longest walk at LGA even with the earlier detours.

Delta waited to long to address the Terminal 2 closure requirement and was forced to a build a temporary structure and still does not have enough capacity when anything goes wrong. The new Terminal 1 construction makes apron operations a mess with a lot less space. Even if the gate is open it can take 30+ minutes for traffic to clear. 30+ minute timeframes from landing to a gate is the norm. While the terminal construction is still underway, LGA now has a lot more taxi and ramp space and operationally much better than it was a few years back. And public transportation to LGA isn't all that bad either with the Q70 - if I have the time I will often take it and find it just as reliable as Airtrain.

I can't say too much about EWR. Living on the east side of Manhattan I just prefer LGA. Outside of international flights or domestic flights outside of the LGA perimeter rule, I don't see why anyone would voluntarily pick JFK.