Asiana Club - Old Gold or New Gold?

I understand that you can 'choose' which membership tier you want.
Right now I'm at 30k mile including 12k from before 2008 rule change.

so I'm about 2k away from New gold but since I'll be taking a round trip (12k), I can qualify for old gold (40k) after my next trip.

Please check if I get it right. Under this scenario I'd be receiving
1. New Gold card after my first flight
2. I'd be able to request for old gold card after my return flight (not automatically issued)

If I'm right, which card do you recommend?

You actually can not chose. OZ will apply whatever rule is favourable. And the first one to kick in will be OZ*S under the new rules. After completing all of your flights you are just 10k miles away from OZ Diamond.