Japan was the first (only?) place I've been where the taxi experience was comparable to Uber/Lyft. Every payment method accepted, apps, GPS routes, non-hostile drivers, and clean vehicles. It's no wonder why ridesharing companies have failed to gain much market share there.
Some of my very few pleasant experiences were in Japan. I don't doubt that Singapore would be fine too but public transit was generally faster there so I never took a cab.
London definitely has a better standard of cars and service, but they will still try to take longer routes and play games with you if you're obviously a tourist. Definitely better than most places though, their standards for cabbie training are very high.
Yes, same here for Japan and Singapore. Drivers super polite and never, ever tried to cheat me. I cannot say that from almost anywhere else, at least ocassionally or more than that tried to cheat.