I believe London taxis also have a good rep but haven't use them.
On the other hand I've had criminal experiences in Istanbul and Rome and non-pleasent experiences in LA and SF.
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.
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 black cabs are great, but the cost is so high most people take mini-cabs which aren't.