I've visited Berlin myself last Summer and I know people who spent six months in Beijing studying. From what I've heard, (granted, not a lot) Beijing is a pretty cool experience but the English literacy is quite disappointing outside of the campus area. Harder to settle down, especially compared to open and internationally-oriented Berlin. I'd love to spend time there but I personally wouldn't move there, unless the research alone is enough reason for you. Hong Kong is really cool. 9/10 would recommend.
I gotta do some digging around and see what's available, for sure, to see if it would be worth my while. HK vs Berlin? Whatcha think? ...unless the research alone is enough reason for you.
Now that's a more difficult choice! It really depends on what you're looking for. Berlin has more history but Hong Kong is more insane. Berlin is much cheaper to live, especially the rent. But if you can find a place to stay, Hong Kong has much more to discover, with beaches and culture just a bus / metro ride away. Either one would be great to visit, so why not visit both?
Both is the dream, and the long term plan, for sure, but your small comparison list is what I was going for :) I'm def leaning towards it a lot more now, just gotta avoid the smog, is all. Plus getting to take a ride on the high speed rail seems too good to be true.