Since we are in Philadelphia, PHL is our logical home airport, though we have left from Newark a few times. Philadelphia is limited, only about 14 airlines, and the main player is American. United and Delta do not fly international from here. As for Lufthansa, they have exactly 1 flight per day from Philadelphia--to and from Frankfurt. And we have taken that round-trip 6 times since we started traveling 11 years ago. We have been happy with it, their cabin service is excellent, they even use metal utensils, several trips with the beverage cart, not just at meal time, wine is complimentary. Except for one year they use an Airbus 340 for this route, seating is 2-4-2, so you never get a middle seat. The food quality on the plane is better coming inbound from Europe, I have always attributed that to the food put on the various flights of of PHL is serviced by Aramark, and I have never liked their quality (they also have a monopoly on our sports venues, and franchised chains have to get supplied by them). Regarding Frankfurt airport, for all the complaints here over the years about how huge it is, if you are simply doing a Lufthansa-Lufthansa connection it is very straight-forward, not terribly far apart. and well signed. Clean. Along with restaurants there are several bakery/deli chains that are not overpriced with good quality food. We generally count on a good breakfast when we are outbound. We have found the customer service in Frankfurt Airport, at least as Lufthansa is concerned, and that is LH's main hub, to be excellent. On the late inbound flight that I mentioned, most people with connections were taken care of before they even left the plane. We were directed on entry that our gate was not yet closed and we hoofed it. They even assisted us in getting off the plane ahead of the crowd, at least they tried to, but since we did not gate and had to board a bus, it pretty much did not matter.
Flying from US to Europe, you are pretty much assured of needing a connection, unless you are flying into that specific city. Lufthansa will land in Frankfurt or Munich, BA in London, American has several gateway cities, Delta I assume will go to Paris, SAS to one of the Scandinavian hubs, TAP to Lisbon, Turkish to Istanbul, and so. And then connect on their network to your destination. We once flew into London by overshooting it on Lufthansa into Frankfurt and then jumping back, but our return was then out of Amsterdam, and Lufthansa, even with the "wasted" miles (they would not stop and let us off in London as we flew over it) was still the best overall routing and flight.
Noting Badger's comment, I believe Lufthansa is always rated in the top 10 (which includes no American Airlines), just behind the Arabian luxury carriers et al. Or to us, the top-rated airline that we would actually be using.