You can use a variety of different cars for the Taxi mission.
You can use the normal Taxi, a yellow car with a taxi sign on top which you
can find literally anywhere. Then there is the so called Cabby. The normal Cabby
and the Kaufmann Cab. Both are slower than the normal Taxi. Later on there is a special
variation of the Cabby to be found called the Zebra Cab,
but you get it so late in the game so that it is not worth it to wait for it to do your Taxi driver mission.
So I recommend the normal Taxi for this mission.
What do you do
You have to pick up 100 passengers and take them to their destination.
The time management is very easy. If you are fast enough and have time left over after you
dropped out your passenger you get this time added to your time for the next passenger on your way to 100 taxi fares.
Other important stuff
Once you drove 5 passengers in row without totally wrecking your Taxi or getting out
of the car (which would end the mission) you get $500 extra. For 10 passengers in a row
you earn $1.000 and so on every 5 passengers.
If you are really fast you get a speed bonus.
If a passenger gets out when the timer hits exactly 0 the time gets turned off and you have unlimited time.
When no more passengers want to get into your Taxi because it is so wrecked you can get it repaired at a Pay 'n Spray.
Do this to keep your current passenger count active and earn more money every 5 passengers.
Sometimes Haitians seem to not like to travel by Taxi, so don't worry if you can't find a new passenger once you dropped of your last guest at Kaufmann Cabs or
at the Pizza Restaurant in Little Haiti. Just get back to the main street.
When you are driving with the Zebra Cab your passenger won't complain
if you need too much time. Also the Zebra Cab is a bit faster and can take more damage than the other Taxis.
You don't have to drive your 100 passengers in a row.
To get it done somehow anyways get a sixpack and take a sip of beer after every delivered passenger. After about 50 passengers it gets really funny but also
harder to control the Taxi. If you don't like alcohol, this also works with 100 pieces of chocolate or 100 gummybears. Or challenge yourself to only drive on
the left side of the road.
But you need to drive 100 taxi fare passengers at all for the 100% completion of GTA Vice City.
For 100 delivered passengers you earn the taxi booster. You can do very funny stuff with the taxibooster,
you have to wiggle you taxi around before and then drive against a wall with an angle and stuff, there once was a good explaining video on youtube but
it got removed so here is a video of all this in action but sadly without explanations: