Taxis in San Francisco are only at their best if you are in and around downtown but then you better have a good reason to use one! Most downtown locals walk everywhere or take the bus unless you are dressed up or have something heavy to carry.
In the rest of the city it's hard to find a cab unless you call one and then it's so expensive to get across town. The city is only seven square miles, it should not cost $18 to get from one end to the other.
Cab drivers in NY city are awesome. Fast and cheap compared to here. I have never taken a cab in Los Angeles, you need to rent a car if you don't have one. The cost of taking taxis would be outrageous. I lived there for five years and never knew anyone who used taxis. I have taken taxis on two occasions in Tokyo. The first was a damn nightmare! He had some nerve charging us anything after getting so lost that many times going from one neighborhood to literally the next one over. The second time was after a typhoon and there was no other choice to get to Tokyo station. That was thankfully a fine ride. But I assume every driver can find Tokyo station!