Virgin Atlantic would be my first choice
Although British Airways has more choice (two flights a day). I'd pic Virgin Atlantic. Oh and an upgrade to Premium Economy if you wanna spare that extra bit of cash.
Virgin Atlantic's v:port entertainment system is bliss. On my 10hr flight to SFO
i was on my entertainment for all the flight and it went in what seems like less than 5hrs! Premium Economy is great upstairs. You have just a 2-2 configuration and it seems very quiet (as there are only like 4/5 rows in Premium Economy and then like 3 rows in upper class at the front of the upper deck). If you want your bag when the seat belt signs are on, but don't wanna put it by your feet, you get an extra compartment between you and the window where you can put your stuff in.
Also if you have people in front who are like family or friends or whatever you can stretch your feet out over the compartments. You get leg rests, footrests, Tables that come from the armrest, a very wide gangway so even if there are trolleys there you can still get to the loo. You're greeted with Champaigne, Bucks Fizz or Orange Juice.
If you're going in upper class, well it'll be home from home. They have the longest flat bed in the industry, a massage room, an onboard bar and loads more.
I say Virgin, and if you do have that extra cash to spare then i recommend an upgrade to Premium Economy. It's shouldn't be too bad for december. When i looked it was just £3000 for four people in Premium Economy