I would certainly recommend the A380 in F over the 777/747 - it's considerably more spacious, and the service seems a little better, too.

One point to conside if you're not a frequent F traveller, only JFK has a Concorde Room outside LHR, so you might want to sacrifice A380 to visit that pre-flight if lounge surfing is your thing.

Another factor (though not really compatible with an extensive lounge surf) would be the eastbound day flights out of JFK (and BOS?) departing around 0800 which allow you to enjoy the service on board without feeling you should really be asleep. Also help massively with averting jetlag IMHO.

Be sure to try the Pudding Wine, use the Concorde Arrivals Suite in LHR for delicious smoked salmon scrambled eggs breakfast, and request a bath not a shower and follow the other tips in this thread:

http://www.flyertalk.com/forum/13303132-post21.html