I'm in Australia and am currently with TK but considering a change to OZ.

I like TK because it allows family pooling, so travelling with my wife once a year Australia to Europe in Business Class is enough to maintain Gold with TK (and OZ) and thanks to family pooling builds up a meaningful balance of points to use for something useful before they expire. Asiana has much longer expiry window. So I suggest you do a quick spreadsheet of your anticipated travel and see if you meet the threshold with either program. It depends what is most important for you. I value Gold and it's benefits way over redemptions. (OZ also has lifetime Gold available.)

If you use Booking.com you can earn TK miles with each booking. This probably isn't as valuable as the free nights available with Hotels.com but if you travel a lot can add up.

For an Australian some extra things to consider are OZ flies to Australia so might give you better benefits and redemption options. TK has been talking about flying to Australia for years but still hasn't managed it.

Customer service with TK is notoriously bad (but their Australian sales office is excellent and helped me through a redemption very easily). I don't have experience with OZ customer service.

I'll qualify for TK Elite (Gold) again and my membership year finishes in September, so I then have to make the difficult decision whether to swap to OZ or not.