Everyone has already highlighted the differences between the in-flight products. Which is in coach pretty much the same.
As for LHR vs LGW. What I find interesting is that Gatwick has far better rail connections than Heathrow. LHR only has Heathrow Express to Paddington and is at the end of the Jubilee line on the tube... good luck lugging your luggage onto the tube. Whereas Gatwick is on mainline rail. Gatwick Express runs directly to Victoria station for 11 pounds each way. Plus Thameslink runs to London Bridge, Blackfriars, Thameslink, Farringdon, and St. Pancras... much more convient if you have business within the City of London or the Docklands. Plus you are on a mainline longhaul route on Virgin trains... which means direct service to Oxford and Birmingham, certainly not more than one change.
But then it ultimately comes down to what ticket is cheaper.
Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia