Welcome to FlyerTalk.

Please answer some of the questions below - as this will make a difference in the answers.

Which airline do you normally fly on - Thai or Asiana?
Which class - business or economy?

The answer is generally go for the airline that you fly the most on as they give the most benefits.

Asiana also has the advantage of family pooling - so if you have family members that fly infrequently, then rather than have small amounts of miles sitting in lots of accounts - they can be pooled to get a ticket easier.

Thai gives you upgrade vouchers once you make gold and have generous two year qualification periods. Asiana points never expire, so if you never quite make it to Star Gold on Thai, chances are you will with Asiana.

I hear that Asiana doesn't have very good earn / burn ratio's. So you might want to check again which has the best ratio for the reward that you want.

Lastly - being based in Korea, you are likely to be able to get credit cards there that will give you extra points - this could allow you to earn faster.

It really comes down to the two questions - who do you fly with the most and in what class.