One great tip for LON NYC flights is to always include a Saturday night in your stay - otherwise the fares go up massively because you're seen as a business traveler (e.g Monday to Friday)
Use The BA Source website to see aircraft used by flight number. Although since you're planning December, it is a bit useless as aircraft may change between now and then for that flight.
Generally, fares in the £400-500 for economy return is pretty good. Norwegian and Primera are cheaper, but you have to add on food, drinks, luggage, etc. But free wifi on Norwegian!
Overall, I find the AA planes easier to sleep in compared to BA or Virgin.