I'd definitely recommend Birmingham as well, I always fly into it instead of Heathrow or Gatwick since my husband lives in Northampton. I found it fairly easy to navigate once you touch down, and passport control/customs is fairly decent as well. Depending on when you actually fly into Birmingham you might be able to skip huge immigration lines--I find it pretty empty since my flights always get in sometime around 6-7am, though my longest waits have been to claim my luggage moreso than immigration. When my husband used to travel to the States he'd have to take the trains back into Northampton and he said it's not too difficult to catch the train from the airport (though I can't vouch for that myself, I've never taken the trains yet).