Where is the best place for shopping in Hongkong and why?

If you are looking for bargains, try the Temple Street Night Market. As the name suggests, don't get there before 7 - 8 PM.

You might also try the Stanley Market on Hong Kong Island. The last few times I've been to HK, I have not bothered going to Stanley but its worth seeing if you have never been. It will take at least half a day to get there, shop, and return, but the bus ride has some very pretty sights.

temple street

http://www.citygateoutlets.com.hk/index.html

a large outlets mall in HK.......located in Tung Chung. just take MTR to the Tung Chung Terminal.

If it's between the three place, I'd choose Mong Kok. Mong Kok is more catered to locals, whereas Causeway Bay and Tsim Sha Tsui is more for tourists (they are more of a touristy place). If you're buying clothes or shoes though, then stay in Tsim Sha Tsui and Causeway Bay, again because they are more for tourists, they usually have larger sizes.