Both would be good.
A lot will depend on how big you are.
If you're less than about 5'8 and maybe 180 pounds it probably makes little difference. If you're tall or fat or both you'll find that some airlines are reasonably comfortable while others are like purgatory on wings.
Personally I won't fly BA if there's any option at all (and not going is preferable to flying BA). If it's the only option and I needed to fly BA to something like my father's funeral I'd consider it, otherwise I won't fly them at all, ever, without exception. Their planes are so horrendously uncomfortable for me I just won't do it. I found a $600 economy class seat from US Airways significantly more comfortable than a $3000 seat in BA's Premium Economy. Sure, BA gave me a little extra room but the design was such that I couldn't use it, and at the end of the flight my neck and back hurt because none of the adjustable features of the seat would adjust in a way that was comfortable for me. Any time I'm talking to a travel agent it usually takes several attempts to get it through to them that I don't want to fly with BA, and if BA is the cheapest price I want them to give me the second cheapest price.
Since US Airways got absorbed into American Airlines I tried AA for my last transatlantic trip. It wasn't quite as comfortable as US Airways but passable. I'd fly with AA again.
ETA: Obviously it will also depend on what route you're taking and which airlines cover it efficiently. US Airways was convenient because it offered direct flights between the airports I wanted. If you have to start changing you have to decide whether the time is worth the money. Personally I'd rather just pay an extra $50 for a direct flight than reroute via some other airport, spend four hours kicking my heels and have to deal with disembarking, customs, potentially clearing security again, embarking, and creating another point of failure for the trip.
I'm about 6'5 and 250lb so space is important for me.
