Academically, HK is as competitive as any other universities in the States, particularly in the medical field. It is true that certain universities in the States may have more fundings and better facilities, but that's down to university-to-university comparison
If you're already studying in the States, you may find yourself more comfortable with the universities there of course. Personally, I encourage young people to spend time in the world just to get International exposure, and you can seriously appreciate the difference years later.
Why do your parents want you to study in HK anyway? If it's just because they want you by their side, you have to let them know that you're an individual person. And no matter how much they love you, they have to let you grow. You have to consider their feelings as well though, by proving yourself to be mature enough.
Yet, if there are other reasons, like if somebody's health is of concern, then it'd be completely different. Afterall, family is the most important thing in the world.