Best European route network, best schedule, best hubs, best connections in the US, great maintenance, good fleet, wonderful and professional F/A´s overall just a very professional and great carrier!
All other US carriers are ok as well and I would take them in the following order:
I would prefer a US carrier over any European airline, because I think they´re just much more professional and the F/A´s just have a lot more personality and seem to be more passioned and skilled!!!
They sometimes might be old, but F/A´s at European carriers just can´t beat them in kindness and professionalism!!!