The rankings are done in terms of discrete client industries or areas of legal practice, e.g. aviation finance, shipping, project finance, competition law, construction litigation, capital markets etc etc.

For that, you need to do your own homework and look @ industry publications like Chambers & Partners, Legal500, IFLR, AsiaLaw profiles, or Asian Legal Business.

This isn't like secondary school or JC anymore where you can rank which are the top schools and which aren't, or, as people on this forum seem to have some childish obsession with, law school rankings.