In terms of differences onboard, with the exception of the seat I believe they are slight. I did JFK
in F over the summer and significant cutbacks that differentiated F catering from J were made early last year.
The J seat is very similar to international J seat but with less recline and less pitch IIRC. The F seat is a nice big armchair job and reclines to almost flat. I found it very comfortable for the 5hrs or so onboard. Also bear in mind full fare F (as opposed to A) and award tickets gets you Admirals Club access at JFK
If you are familiar with the J product then this may help with getting some idea of what F is about:
AA Flagship Service: JFK-LAX In First Class (pics) (by Fbgdavidson Jul 12 2006 in Trip Reports)
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