I absolutely understand where you are coming from. I immigrated from HK when I was 15 and am currently enrolled in a MD program in the US. Trust me, either choice isn't going to be easy. So let me try to break it down what I have experienced or heard from my friends working in the medical field in HK.
1. HK is and will continue to be politically unstable. That being said, there is also a good chance that the med council will allow more mainland doctors to practice in HK. I personally don't know any mainland doctors, but from their medical documents that I have seen, there are quite some discrepancies from our guidelines. So honestly, I cannot fathom how it would be like once the laws have passed.
2. You still can return to HK if you'd like. You just have to play by their rules. I've heard the med council is recommending some kind of 5 year internship? So again, very dependent on politics.
3. I believe that there's more diversity here in the US because of the immigrant population. For instance, my friend, who is a medical student in HK, told me that they have never seen a sickle cell patient before, while it's extremely common in my university hospital. So medically or for knowledge wise, it may be worthwhile to consider coming to US.
4. Leaving HK is going to be hard because you know you are able to end up here in a US medical school ONLY because of HK taxpayers and the free education that comes with them. I hold this to my heart very dearly every day and it is not easy to cope with. You are going to feel homesick, especially when things escalate in HK. But it's never a one-way road in life. For example, I consider both HK and US my hometowns - one in which I was raised, one where I spend the majority of my adulthood. So I'm going to help out whenever these two places are in need of my service. Now, I am seriously considering practicing in HK when I'm done with my medical training, because of the severe shortage of physicians there. OR in contrast, it's never too late to start your career in the US. You can potentially start it when you have attained your medical degree in HK.
Those are my honest opinion. I hope it gives you some insights.
What do you mean by pre-clinical medical student? What year (out of 6) are you in or have you already graduated? Your options may change depending on which year you would be put into when you are here in the US. Feel free to PM me!