I assume you are wanting to travel back to HK and work there? If so i would strongly recommend you to accept HKU's offer and stay in HK.
For one, durham is a good university, but it is not that good. Most people in HK would have only heard of universities like Oxford, Cambridge, UCL, LSE, Imperial... Durham,not so much... Whereas HKU, everybody would have heard of it in HK, as it is the top university there
Some people would mention rankings, (so i might as well mention it now) according to the times Durham is ranked 122 in the world, compared to HKU which is ranked 26; now a lot of people will tell you ranking tables means nothing, but in fact they do mean that a university is generally better precieved by employers and students alike, as times is based heavily on peer and employer's review.
Secondly if you want to work in HK, study in HK, as you'll be able to build up your contacts during your university years, and will be able to find your way to the top easier later on