In an ex Taichung and Taipei residebt as you know. Truth be told I’ve never made a lot of friends in either locality and don’t think the denizens are all that friendly. Taipei has a great range of neighbourhoods to visit connected by the MRT surrounded by great hills and bike trails for hiking and biking.
Taichung I enjoyed for its sunny weather all year round , it’s more open space (although rapidly developing),
cheaper housing , slightly slower pace of life and the fantastic access to the rest of Taiwan on any given weekend (I spent many weekends buzzing around random mountains in Nantou and Chiayi). Taichung has some very high quality neighborhoods to live in with quality new housing often stand alone houses , that you simply with my find in North Taiwan. If you have kids you can send them to kindergartens and schools with ample outdoor space, not prison like conditions like kindergartens in Taipei area. Taichung is indeed a bit boring but it’s still way more interesting and liveable than the commuter suburbs of Taipei or Hsinchu. Oh yeah Taichung also has fantastic tea and tea vendors , unfortunately many of the famous tea houses have closed . I learned a lot about tea living there .
But I agree that Tainan and Kaohsiung feel more like the 'real Taiwan ’ , especially Tainan , which after all was effectively the capital city of Taiwan for centuries. Fantastic range of restaurants there actually although public transport is lacking so need to be able to ride a scooter possibly .Some fascinating neighbourhoods .
Kaohsiung also has some great parks and the harbour, the part that lets it down is the heavy industry (not everywhere but some areas you need to completely avoid ) and traffic on the highway and the driving on the sidewalks. Air quality is a real concern .
Last point. In terms of earning money it’s very very hard for ‘business professionals’ to find a well paid job outside of Taipei or Hsinchu. Taichung…Almost impossible. I tried and wasted my time and money and had to leave the city. If you a teacher or business owner it might work out better in places like Kaohsiung. Or if you have a remote gig, yeah.