BMI and Asiana look like great options within *A for those looking primarily for lounge access. The rules for achieving the level equivalent to *Gold are a bit more complex than for the North American airlines, but it'd be worthwhile for the OP to carefully read the rules for all of AC, BD and OZ, and consider his (or her) flying patterns before choosing one. If you can flying the carrier's own metal for at least some of the flights, you may also be able to take advantage of some upgrades.