It was near the top of the list, but failed on two big counts:
(1) - the air
(2) - Cantonese
I've already been studying Mandarin slowly for a couple years, and though I've heard I could have "gotten by" with English and Mandarin, I really wanted to just focus on Mandarin + simplified Chinese.
I've been in HK for the past 2.5 years. The air isn't too bad. For example today, sunny and clear skies. I think it would only have a measurable effect on health if you were to live here 30+ years. I would say in any given week, maybe 1-2 days it's slightly smoggy here.
Singapore is a good choice though. I've also considered it. Some may complain about the hot/humid tropical climate all year round but I like that. It's also the most racially diverse country I've visited. Given your wife is Indian she will have an easier time settling in there than in HK where it's predominantly Chinese but with a huge expat crowd on the island side. Cantonese is not necessary here, you could get by without a single word really as most people speak English and Mandarin here. There is probably more chance of getting some Mandarin practice in too than in SG where they speak a variety of Chinese dialects.
It's far easier to migrate to Singapore than Hong Kong. At best you'll be able to get residency after 7 years, but that's only if you can manage to get a work visa, which is not easy unless you work for a big company.
I lived in HK for 10 years and will go there every other month. I love HK. But it's not for everyone. People there say you work in HK you don't live there. And that's all you do, work, work, work and then take a break to do some other work.
After 10 years of 18 hour days 7 days a week, I moved to Thailand and for the last 12 years. I live 50km from the Laos border in the city of Udon Thani. I see trees and the occasional elephant from my room.
I live here and then run my business from other countries like Hong Kong and Singapore.
I like Singapore. Unlike Hong Kong they actually welcome people to migrate there. I will move all my operations there over the next year or so and get residency and then split my time between Singapore, Thailand and Laos.
BTW, Cantonese is a far more more interesting language than Mandarin. Mandarin is a second language for a large percentage of mainland Chinese. But it's good to learn for business. And in my humble opinion, simplified Chinese is an ugly hack from a committee that has stripped most of the beauty and meaning from the language. If you learn traditional first, simplified is easy to pick up and you'll understand the context and meaning behind the characters. Compare the simplified and complex characters 'country'. The traditional character tells a story, a country is a place with a border, which is defended with weapons and words. The simplified charger is literally, jade in a box. Yuck.
(1) - the air
(2) - Cantonese
I've already been studying Mandarin slowly for a couple years, and though I've heard I could have "gotten by" with English and Mandarin, I really wanted to just focus on Mandarin + simplified Chinese.
But mostly it was the air. :-)