As you're sensible enough to realise neither is a true long term option, ask yourself which will leave you in a better position when it's time to move on.
QATAR - Heavy time with possible upgrade
Korean - Medium time with no upgrade
Whilst commuting with Korean may be more attractive than living in Doha, think long term. Unfortunately neither offer an ideal working environment, particularly for an F/O.
BTW Perfectly reasonable of you to ask on two different forums being as each of your airlines is located in a different part of the world. QATAR pilots may not read the Far East forum and vice versa.