I've split taxis between the large fleet yellow / checker types that are now just pods running on Grid Guide and Gypsy cabs which are self-employed drivers. That way the nice clean areas of a city are well served by swarms of silent-running pods, but they will not take you into the seedier areas. You want to go to the Barrens, you need to hope that the cabbie hasn't been smoking deepweed before picking you up!