I have a 7 hr layover in JFK before going to Barcelona.. what is recommended that we see during this time?

By public transportation, it takes a good 2 hours to get anywhere interesting from JFK. (Use this site for the best directions, unlike Google, it takes into account service changes and it's surprisingly accurate http://tripplanner.mta.info/) Since you need to be sure to get there roughly 2 hours in advance for an international flight, you have to add time to get out of the airport and to public transport, you could be delayed, and you never know about transportation problems, it'll be pretty tough to see anything. Possible, but tough.

If you get a cab, you can reaslistically get to and from Coney Island. That'll be more like 1 hour maximum, depending on traffic. I would guess that would cost you $50 each way, maybe less. You might have trouble getting a cab in Coney Island, call a cab company (212-777-7777 and 212-666-6666 are ones with easy to remember numbers who specialize in airport runs. You can call now and find out the price and book your round trip ride. They can be tough to use same-day. I don't know the local cab companies in Brooklyn that you could call same-day, I only know the ones in my neighborhood.) In Coney Island, ride the Cyclone, see the Freak Show, eat at Totono's Pizzeria, and the original Nathan's, walk the boardwalk, play some games, etc. It's not what it used to be, but it's historic and still fun.

The Shuttle Buses to midtown take only a little longer (1 hour scheduled to Grand Central, probably about 2 hours from your scheduled landing time to getting off the bus). That should leave you with a solid 2:30 to 3 hours in midtown (they run every half-hour, so that may add to your transportation time if you get unlucky). You can see Times Square, maybe Grand Central too. That'll run you less than $30 round trip and is probably worth it.

http://www.nyairportservice.com/page.php?id=48

LGA is a lot closer to the center of the City than JFK.

Not a Coney Island, there are nothing to do there anymore, 3 rides, that is all. Explore JFK, great shopping, there is a mall not very far away with Target, not sure if they have bus from JFK.

The best idea just to wonder around, you do not have much time to go anywhere.

I'd go with Coney Island. It's 16 miles from JFK to there. Be sure and prepare for wicked traffic during rush hours. If you end up staying at the airport, there is some art museum at terminal A. Next time I get laid over there I plan on checking that.

7 hours really is not alot of time to go sightseeing. You can ride the air train for awhile, its free. Check out the other terminals amenities. Some have nice stores and restaurants.

I would go to Rockerfeller Plaza