Without a doubt, Miami. Florida's a great holiday point in its own right, and much more relaxed than Dubai. Additionally, there are a number of other "spotting" airports within easy striking distance of Miami International.
However, on the downside, then you might have to tolerate BA (meaning Barely Acceptable) service. Personally, over recent years I have avoided using BA whenever possible (all the more since being caught out by their 27 May I.T. debacle!), and by far preferring Aer Lingus to Florida.