Originally Posted by
angetenar
That completely changes the question. At LAX, TK and LH use TBIT and the connection to T7 can be annoying and involve a fair amount of walking. At SFO, LH and TK (presumably) use the G gates so the connection to UA flights is not too hard. At DEN, there is only really one terminal and I->D connections are not too bad either.
I guess 3h transfer time in DEN should be enough. There is 1h30min too and for me it is way too short. 1h 20 min transfer time in IST should be doable.