M.Moose (does the M stand for Mighty?) I really don’t think you have anything to fear flying in a BA aircraft.
Personally, I find the World Traveller Plus seat rather hard for my liking.
The alternatives suggested – Singapore Airlines, Cathay Pacific and Malaysian – do not offer a Premium Economy cabin (except SQ on its A340-500).
WT+ is ideal if you are a couple travelling together as you can have your own pair of seats near the window, rather than having to share the row with a third person, as would be the case in World Traveller/economy. WT+ also, uniquely on BA, has a stand alone seat near the emergency exit on the 747 – you can check http://www.seatplans.com to find out which one.
Apart from the additional personal space, tier points and 125% of miles flown World Traveller Plus (WT+) now has Video on Demand (AVOD) aboard all 747 and most (90%) 777s. As the seats are simpler in design there is much less than can go wrong or become tatty or worn out.
It would be madness to endure an extra flight via HKG on an already long journey; and keeping the whole ticket with BA is much the best plan to ensure smooth connections and ensure you miles get credited to your oneworld account, rather than running the risk of mixing carriers with non-protected connections and heightened baggage loss risk (note you cannot credit BA transatlantic flights to AAdvantage, the American Airlines scheme).
Connections within T5 as your planned BA to BA itinerary should be fine.
Note that WT+ does not get you access to BA’s superb lounges at T5 (unless you have oneworld status) but head up to Gordon Ramsay’s Plane Food for a drink, a meal and enjoy the view of the apron before taking away one of his picnic bags for the sector to ATL and you really will probably eat and drink better than most in Club World:
The man is unnecessarily foul mouthed, but hats off to him for running a successful business and Plane Food is top notch.
As long as you bought your tickets at ba.com you can easily upgrade in Manage My Booking (MMB) either the inbound or the outbound flight with BA Miles to Club World’s fully flat beds, subject to award availability.
You also stand a greater chance of being operationally upgraded (quite rare on BA!) to Club World, whereas buying an economy seat would only usually get you upgraded to WT+.