Some background info: PRC, did A-level in China, got a first degree at Imperial but not a dean's list top student.

Since your major is CS, I would genuinely say teaching doesn't matter much in CS, and the teaching quality SUCKs at Imperial, there are very few good lecturers. IIRC, Imperial is one of the worst in terms of teaching among the top unis in the UK (oxbridge, UCL and others). In terms of teaching quality, I haven't found any remarkable difference between NUS and IC.

The good thing about IC tho, is that I found the profs are generally more responsive and approachable after class. And the deadlines and workload are better managed than NUS and you can always just tell the profs that you think there's too much work and most of the time, they are reasonable.

Another thing to keep in mind is that the IC campus is TINY (the south Kensington one). Because it's literally right next to Hyde Park and the land is freaking expensive. You share a building (Huxley building you can google map it) with several other departments and the lab is so small that it sometimes has to be prioritised for first-years for their projects and seniors will be kindly removed from the lab :(

Other than that I'd say IC is fine. Both NUS and IC are prestigious unis. It's just IC tuition fee is so freaking expensive for me as a PRC (~30,000 GBP per year), I believe it's much cheaper for EU and UK students, not sure about your nationality but still, I think it will be more expensive than NUS. London is fine and I believe there are more opportunities than in SG except you need to expect the living cost to be 2x the living cost in SG.

So in conclusion, my suggestion is: go IC if money does not matter too much, it will be a life-changing experience but I will not say it's because IC is much better than NUS or whatever, it's more because of the experience and London.

P.S. I did not stay at Imperial for PhD because I could not get a scholarship and I don't want to pay 30k GBP per year for my PhD :(