TK is outstanding IMHO. The chefs on the flight and the seats alone are worth the cost. It is usually less expensive as well.

I don't know if you have flown them before, but they have a program where you can layover in IST. It is very nice and IST is well worth the visit. If done correctly, 8-10 hours is enough to see the big attractions (haga sophia, cistern, and the grand bazaar). I know there is a lot more, but those are worth the visit.