If you're starting out and wondering which authority's licence to do for an easy conversion with a view to working in HK, don't chose the FAA licence. You will have to do lots of exams in HK as the FAA computer testing system is deemed to easy. The JAA sexams are very similar, as are the Aussie and NZ ones. I would chose the Aussie system. But for cost, look at South Africa as well. The exams there are of a very high standard and I'm sure they get favourable reception in HK.
But to convert an ATPL to HK ATPL, you need 2800hrs with 500hrs on suitable commercial aircraft. If you don't you will be issued with a CPL.