To reach the center of Rome from Fiumicino and Ciampino you can make use of all types of transport, from the most comfortable in the cheaper ones.
Trains depart from the airport of Fiumicino, private shuttles in agreement with their airlines or bus if it is the airport of Ciampino, all leading to the center of Rome.
Only a speech exception is made for taxis. The output of the airports you can stumble with taxi drivers unauthorized trying to bring in the central areas of the city to non-competitive prices. It should be known that taxis are white cars with Taxi table at the top of the car.