Lived in Taipei for 5 years after having lived in Hong Kong for 5; have now been back in Hong Kong for 18 months.
If it's relevant, I'm a single caucasian female who speaks both Cantonese and Mandarin.
While there is a big variety of beautiful places in Taiwan compared with Hong Kong, I absolutely loathed living in Taipei because
- bureaucracy for foreign residents! The situation has improved, but HK is still much more streamlined
- except for a few showpieces, upkeep of public areas (specially parks) was appalling.
- sidewalks just about unusable - not just mopeds parked all over, but steps, broken pavement, drainage ditches, shops extending half way or more across, etc... (OK, Tien Mu is better than downtown).
- unlike a previous poster, I found the city layout thoroughly inconvenient. I had to waste so much time just getting from point A to B to C. (and I live in Tuen Mun now!)
- driving is definitely worse than in HK, as are construction standards.
- typhoons & earthquakes (those construction standards again).
- I found the people there even more face-obsessed than those here: for instance, if I asked directions in Taiwan, people would give a made-up answer if they didn't know; here they'll just say they don't know.
- the ready acceptance of violence - domestically, politically and even among different sects of Buddhist monks. There's still huge antipathy between "native" Taiwanese and "mainlanders" - nearly all the descendants of the latter now, and let's not even mention the first nations of the island.
- and generally I just found the residential and local commercial areas of the city to exude a dull, grey sameness.
It wasn't ALL bad; I did like the street market around ShiDa, and appreciated the efforts being made to encourage recycling even though my job meant I was only able to get to the rubbish trucks once a week, which meant my "real" rubbish got distinctly on the nose during summer.
But I have NNNOOOOOO regrets whatsoever about moving back to Hong Kong