<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by eye on american:
You might also want to consider Turkish Airlines. If you use Turkish, you have a lot more options on AA for the transatlantic flight because all you need to do is get to any European AA city and pick up Turkish from there (increasing you odds of upgrading). LHR, CDG, ZHR, FCO all work -- Brussels should as well -- not sure about Madrid. You can earn AAdvantage miles on Turkish as well and the AA Agents can book the tickets for you.
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I'd stick with BA from LHR to IST. If you fly Turkish Airlines, the miles would not be elite qualifying and you wouldn't get the Platinum bonus of 1,560 miles each way. Moreover, you wouldn't have lounge access when flying economy before boarding your flight to IST since Turkish is not a oneworld alliance member.
If you are going to IST without making a stopover and just doing a transfer in Europe, a hot shower is very nice after an overnight transatlantic flight. I believe the BA Club Europe Lounge at terminal one has shower facilities.
But if you don't care about lounge access or earning extra miles, otherwise, I heard Turkish Airlines offers good service.