I have a different view on cab drivers versus waiters.
I generally pay 15% tip if I think the service is reasonably good to waiters, but no way I will pay that much to cab drivers.
The reason is simple. I pay for the food in restaurant bills and tips in compensating the waiters for their service. When it comes to cabs, I pay for the ride, that's all. The driver doesn't give me extra service beyond taking me to the destination, which is the fare, so what is the tip for? I will never pay $14 tip on a $36 cab ride. You may be generous but I think it is excessive. We should never recommend it to anyone. If the driver had helpped me with the luggage etc, maybe $4. If nothing at all, I see no point in tipping the cab driver as I don't find the reason too. Cab drivers are unionized, well paid and have very good job security. Can't say the same to waiters.