Air quality - This is a no-brainer. There's no comparison. The air in Hong Kong is notoriously terrible. The air in NYC is not as good as the suburbs but is still a million times better than HK. In NYC, you can see objects that several blocks away just as clear as it is if it was several feet in front of you. In HK, the traffic signal across the street from you is already blurred by the smog.
Blue sky - The natural color of the sky is blue. Yet, I don't remember the last time I saw a blue sky in HK. It's almost always a gray shade. I bet that the young children of HK are confused as to why they're instructed to use a blue crayon to draw the sky when it's almost never that color in reality.
City layout and design - The layout of Manhattan is simple yet genius. Streets are in a grid layout and are numbered sequentially. Street name signs are exactly where you would expect them to be (ie at corners of every intersection). This results in several positives. It's almost impossible to get lost because you know exactly where you are geographically just by knowing what street and avenue you are on. Air passes freely through the city since there's no obstruction due to the grid layout.
Hong Kong is not like this. The primary reason is because HK is mostly mountainous and only a tiny portion of the shores can be built on. So, roads are curvy and buildings obstruct all air blowing through the city. Every street has a proper name so unless you've memorized every street's location, it's pretty much geographically meaningless. Every street's sign appears to be randomly placed so you sometimes have to search the entire block just to know what street you are on. Sometimes, it's on 2 poles; other times, it's screwed to the side of the building; and then there are instances where it's just non-existent.
Highway design - On highways in the US, you are prompted at least a mile beforehand when an exit is coming up. In HK, you are prompted right at the exit. That's just silly.
Pizza - NY pizza is famous. So it would be unrealistic to expect HK to have pizza of NY's calibur. But the pizza in HK isn't even close to being acceptable. Pizza Hut, not enough mozzarella and not enough tomato sauce. Everywhere else, you can't even really call it pizza. It's just toppings with cheese on some sort of bread or cracker. The best pizza in HK can only be found at Terminal 2 of the airport at Familia's. Compared to NY pizza, that's HK's Familia's barely deserves a passing grade. But at least it's decent pizza which is more than I can say for anywhere else in HK.
Bagel - I've not found a single decent place where I can get a good bagel in HK. Starbucks serves frozen bagels. Pacific Coffee seems to bake their own but then they put it on a grill rather than a toaster to heat it. Such a waste.
Hot dog - Sour kraut, onions, relish, ketchup, and mustard. These are the toppings that belong on a hot dog. Not mayo, tomato, cucumber and thousand island dressing. The only place in HK that has the correct toppings is New York Fries but they severely overcharge for it.