What's the difference between all the taxis in San Francisco?

I would say the revenue & outfit (size) would be a determining factor in quality of service. This would be very important for me, as I have been hit by a out-of-town taxi on my motorcycle, ouch!

The car might also be a hint on establishment.

In terms of affiliation, this list helps.

Some info regarding dispatching.

In the United States, there is a Taxicab Radio Service with pairs assigned for this purpose. A taxi company can also be licensed in the Business Radio Service. Business frequencies in the UHF range are also licensed in pairs to allow for repeaters, though taxi companies usually use the pair for duplex communications.

Some companies don't operate their own radio system and instead subscribe to an Specialized Mobile Radio system. The conventional radios are most suited to companies that operate within the local area and have a high volume of radio traffic. The SMR is more commonly used by black car services that cover a wider area, and smaller companies who use less airtime and don't want to run their own radio systems. With the advent of Public Data Networks in the 1990s, operators are beginning to use PDAs and advanced mobile phones for dispatching and tracking functions in lieu of the traditional radio. Some small car services don't use a dispatcher at all. Instead the customers' calls are forwarded to the cell phones of whichever drivers are on duty at the time. via