Hi Carol
I book through American or Delta because I have credit cards that are partnered with them. I believe that I get two rewards per dollar spent at American and unsure with Delta but I do get rewards for every dollar spent. This will go towards my next trip. Often I have been able to fly free because of rewards and I am working towards that for the next trip.
I get one free checked bag with both airlines. And there may be other freebies or reduced costs.
When I last checked American, my fare was $1110.25 with insurance.
I prefer the convenience of flying from Lisbon to Philadelphia . I will go through security / immigration in Philadelphia and maybe be done with it.
I do not like connecting at Heathrow to begin with but I would also have to go through immigration at Heathrow and later in Austin.
I, also, checked out BA and my connection between flights was only 1 1/2 hours. I could not do that.
Of course, I also have to go through security in Lisbon no matter what brand I use.
If push comes to shove, and I wanted to fly Delta, I could stay the extra night in Lisbon. Not a bad thing to have to do.
Also I have a Jet Blue card and Southwest card. I could book round trip to and from Boston on rewards. And then from Boston, book to London and from Lisbon at a lot less money going on Delta or American.
I have a lot of credit cards (too many) because I took promotions.
UPDATE: So I found that I can do round trip Delta to and from Boston. Then Delta Boston to London and Lisbon to Boston, every flight non stop, for about $1400,00 including insurance. Better than $1,900.
I think I am going to do the deed today (book flights) after resting some.
I have to get it over with.