I've flown Korean Air twice, on a domestic route (A300 to Pusan, A330 back). Fine both ways, but as others have said, the safety record is the clincher. I would always fly good old CX (or alternatively, any of the Japanese carriers, Thai or SIA). Ultimately, it comes down to this: how many other airlines do you fly with, where you look out to make sure there's a runway beneath you when you're landing? You sort of take it for granted with others!
Although Asiana has a much better safety record (well, who doesn't), what I have heard from PPRuNET suggests it is almost as shoddy (if not moreso in places) on the safety front as KE.