Overall, I'd rate them like this:

1. HKUST
2. AGSM
3. Melbourne
4. HKU

Obviously, AGSM and Melbourne will be viewed more favorably in Australia - and the Hong Kong programs will be better if you want to work in China/HK.

In terms of US and Canada, it's really hard to say. Certain industries and multinationals with alumni from a particular program might view it favorably - but none are going to have the same weight as similarly ranked programs in the West. I'd suggest narrowing your focus to where you want to work after graduation and picking a school based on that.

True. The rank is quite similar to that in FT / The Economist.
It is the easiest to get into a region where one graduates in. For example, HK/China employers will first look for graduates from HKUST / HKU over AGSM / MBS.
However, being able to work overseas and capturing the best opportunity worldwide allows gradautes to have the most nos. of doors opened to themselves, not only in the short term but also in the long haul. As such, it is considered entering a school which is widely acceptable worldwide will be the best option to me. Of course, one may argue the Ivy League in the States will be the best ticket in this case. However, the right to work/live and availability of financial aid etc currently limit the best choices to the four in the subject line. More comment is welcome.

<blockquote>However, being able to work overseas and capturing the best opportunity worldwide allows gradautes to have the most nos. of doors opened to themselves, not only in the short term but also in the long haul.</blockquote>
True, but international mobility doesn't usually work as expansively as this. This is because even in today's era of globalized business, there are still huge variations in business culture, and those variations, coupled with the lack of a network in a foreign country can severely limit somebody's ability to secure work abroad. This is why the most effective strategy is for students go to a school in a specific region to work in that region. The statistics back this up, even for the schools you're looking at:

A substantial majority of AGSM MBA grads (81%) end up working in Australia, whereas only 41% of them are actually from the country.

Likewise, at HKUST, 88% of grads end up working in Asia.

<blockquote>Of course, one may argue the Ivy League in the States will be the best ticket in this case. </blockquote>
You would think so - but again, the stats say that most grads from ivies end up working in the U.S: only 9% of Harvard grads end up in Asia. 0.2% of Wharton grads end up in Australia.