HKU.
To respond to your specific comments:
1. HKU's business school has a generally weaker reputation compared to HKUST (not CUHK), but only on academics, and fluctuates a lot (so for example, its Master of Finance is ranked Top 5 world-wide by Financial Times).
2. With general academic reputation, CUHK is pretty much the same as HKU's business school.
3. HKU has a way longer history, and a much stronger hold on the politics and business fields than any other local university does (meaning, an overseas qualification would probably benefit you more instead), so in the business field, HKU would be a way better option for the network and prestige.
4. All universities in Hong Kong are campus universities. Yes, many people would say that HKU has lots of scattered campuses, but they are generally not counted (or CUHK would not be able to claim to have the largest campus in HK). As a business undergraduate, you won't go anywhere but the main campus, and in a building or two - business students are probably in KK Leung building. In CUHK, I should think most of your classes should be in a building or two as well, but people do tend to take the inner-campus school buses to move around.
5. CUHK has no historical buildings whilst HKU has a couple on campus; but CUHK does have more green for having more flat land in general. Can't really say there's a 'landmark' in CUHK as a result. HKU is on the hill however, so technically it's close to the green areas all the way up to The Peak.
6. Hongkongers love white people, so you will not be 'alienated' in either places. But you do need to reach out yourself, as they may not do it (in both universities) for language or whatever reasons.
7. HKU has the largest international undergraduate and postgraduate population in Hong Kong - 17-18% of all undergrads at HKU are internationals (on par with Oxford), whilst around 11% are at CUHK (No 2 in HK, slightly higher than Cambridge). With postgrads, HKU has close to 30% with HKUST as a very close second.
8. HKU students and graduates have the highest average proficiency in English, as HKU has been the only university in Hong Kong with a higher admission grade for English, and finalists have an averaged IELTS band 7.1 (same band as native English speakers globally), with business, law, and social sciences students having the highest averages.
9. HKU's halls and colleges are quite tedious in the sense that they expect you to 'contribute' (but some halls leave internationals alone unless they want to join the sports teams, whilst one of them insists on using Cantonese to interview which has been under fire), CUHK's tend not to do anything much and just really are residences. So technically easier to have friends in the former, but depends on how much time you want to spend with those people.
10. A cliquey atmosphere? I'd say the situation should be similar in both universities, and you will always need to make the effort to reach out to make friends. I don't know much about the situation in CUHK, but no international students have complained about that in HKU, though it also shouldn't be overlooked that they could also befriend other Caucasians.
11. The Students' Union of CUHK has been criticised as being heavily left-leaning to the point that they are rather quite foolish; but HKU's does not do anything much at all.
12. In both universities you will meet a lot of mainland students as you're doing business. They may not talk to you much.
13. By the 'busy city', I suppose you mean the CBD, ie Tsim Sha Tsui/Central area. The more westernised bars tend to be on the island, ie LKF (Central) and Wan Chai. HKU is circa 2.7km from Central (on the island); CUHK is 19.3km from Tsim Sha Tsui (in Kowloon). But CUHK has an MTR station (on the East Rail) whilst HKU has not got one (but is expected to have one later this year). Would be awfully difficult/expensive for you to go back to CUHK after midnight clubbing in LKF, but it's not a rural area or anything - Sha Tin, 8 minutes away by MTR, is a big residential area. On the other hand, you would be able to walk back to HKU from LKF. Mong Kok would be a big area (27m from CUHK on MTR; c30m from HKU by bus, but will be faster with MTR) but it's not that popular with expats.
14. Both are sort of on a hill, but HKU is on a much taller one - it leads to The Peak if you go all the way up.
15. Both universities have a strong christian presence as unfortunately it's a middle-class thing in Hong Kong, but CUHK has a stronger one because they have theology.