I usually use public transporation when I travel in large cities because it’s fast, affordable, and convenient! Most of the time be wary during rush hour since it is really busy.
Korea (Seoul, Busan): Subways are the fastest! The bus is conveninet for short distances. Taxis are super cheap.
Japan (Tokyo): Subways are also the fastest! (btw they drive on the left side of the road, so bus stops will be on the other end).
Hong Kong: Metro is clean, efficent like most other Asian countries. Bus is interesting, very British but also works really well. (btw they drive on the left side of the road, so bus stops will be on the other end).
Taiwan (Taipei): It’s really clean, I was only here for 10 hours so can’t say much. Easy to use, and the metro cards are so cute, you can get character keychains at different convenient stores.
Paris: Metro here works well, like better bart. I would say buy the single way tickets, because we ended up ubering some of the times.
London: The Tube is honestly really great, just the prices are insane. Nice thing is you can tap with Apple Pay, but you never know how much it costs (varies by time and area, they have a breakdown). Bus is nice, same comments about the price. But if it is not raining (rare day) then sitting on the top deck and looking around is a great way to vibe and tour the city.
NYC: It’s dirty, but it works and gets you places pretty fast. Tap with Apple Pay (OMNY free after 12 rides in a week). Or you can hop it at your own risk.