I frequent both. CX HK J lounges on average are better.
Food wise, Flagship JFK has limited options - with the exception of 1 visit earlier this year they always have a slightly dry herb grilled or better sauce-flavored salmon, chicken / pork and some mediocre charcuterie, soup and salad - dessert went uphill to mediocre but soft drinks went downhill since opening.
UA Polaris EWR and AA Flagship LAX are better. I guess it's better than The Deck's F&B minus the noodle bar.
I also haven't been blown away by flagship first dining. Heard the burger's good though but never ordered it. Sundae's not bad.
Seating wise, Flagship JFK can feel crowded and less comfortable than say the Pier.
Hope this is helpful.