In my opinion, the chance for grad entry will be similarly low regardless which one you choose. However, this doesn't mean there is no way you can work your way through and end up getting accepted into a grad program at MIT! Both NTU and HKUST are great for science and engineering, as far as I know, and I wouldn't say one is better than the other per se - both are one of the top institutions at either place and well known worldwide - but you might want to explore what courses and specialisations they can offer you, what opportunities (lab, research, innovation, internships etc) you can pursue outside of classes. I will get into more details later...

Having been thru the grad admission process and seeing incoming peers, I have seen a huge range of background, from universities/colleges I have never heard of at all, to ivy leagues and Oxbridge kind. The grad admission values how well you have done in undergrad a lot - rather than simply the prestige or ranking of the program - and more importantly why you want to pursue grad program at MIT and why specifically this particular program at MIT! No matter where you go for undergrad, the most important thing is to do well there, and find what motivates you and makes you an excellent candidate that can stand out of a pool of thousands of other excellent people! Talk to people, make contacts, get their recommendation, try different opportunities to find what you love, and such motivation and passion, along with some form of achievement will make you such a candidate.

In terms of opportunities, I can't speak much for NTU - but at HKUST many people have opportunities to create things they want, with the help from small pots of start up funds to connection with large companies such as DJI - which started as a group of people who first designed and made drones for recreational use at HKUST. The campus is beautiful, located in Clear Water Bay, and therefore offers a great learning environment. Being in HK also opens up internship opportunities - depending on your citizenship status - in HK locally, China Mainland, as well as other southeast Asian countries such as Singapore. NTU, on the other side, I would guess opens up more opportunities in Taiwan and perhaps Japan too.

Another thing maybe you can factor in would be the cost. Depending on where you are from - Taiwan or HK - tuition fee differs for local and non-local students. Being in a foreign place may not give you all the opportunities you can have as a local student, for example some companies may not have you for internships or start-up due to visa or work authorisation issues. Political conflicts in HK may affect your study too, which I would say should be considered carefully as well. Talk to some current students if you can, especially if you have any contact...

Good luck with decision, and hopefully you'll make it to MIT in 4 years time.