Hi John,
We done LGW-SAN ( Orlando Sanford not MCO ) last year on a MyTravel A330, and it was one of the best flights we have done to Florida, plenty of room even in Economy, and still had happy kids after 9 1/2 hrs. Not sure what BMI is like to US, personally i have always been put off by the indirect flights as didnt fancy the extra time onboard.
So A330 gets thumbs up for me, but still does not beat the flight deck visit on a Virgin 747 200 on our 1st trip in 2000, guess thats all history, not to be repeated now 🙁