The demands of civil engineers and BS (Building Services) engineers are quite stable in HK. Engineering firms recruit fresh grad every yr. This yr large firms still recruit fresh grad because gov is proceeding many civil projects in coming 2-3 yrs. Firms need more man powers so the demand may be still strong.
I think civil and BS may be a gd choice coz HKIE provide charter scheme for engineer to earn recognized qualification. The salary and position will be risen after chartered. HKIE also provide scheme to other engineering professions but the salary may not be increased. That means the HKIE charter only benefits civil and BS.
UST engineering degrees requires many assignments and exams. u may feel lots of pressure and stress. UST hv gd connections to Mainland professors and most of the lectures are from mainland. u may feel it's a "mainlandized" university instead of an international one. They spends most of their rescoures in Business school in 2007. I'm not sure if it's the same today. I would suggest u considering which engineering professions u choose in yr 2. u may try to taste all the professions in yr 1 to know wht subject u like most.
If u want to futher study overseas after undergraduate, u MUST get prepared during ur 4-yr-undergraduate life. Spending time to study overseas universities, saving money and learning foreign languages. Also, ur GPA must be bright enough to let those admission panels to consider ur application. 4 yrs may be just enough to get all the things ready. u may check this link for postgraduate study info.
http://library.ust.hk/guides/pg.html
Wish u hv a happy undergraduate life!!!