The fastest route from central Paris is by RER line B train & OrlyVAL shuttle train.
he Orlybus is a good option, leaving from Denfert-Rochereau metro station.
Air France service 'Les Cars', which are actually very comfortable coaches are also an option and you do not need to be an Air France customer to use this service. There are three locations within the city where you can pick up these coaches.
Taxis are the first choice, though an expensive one, of many travellers, as you are taken directly to your destination. This also applies to the shuttle services which allow you to keep the price down by sharing with fellow travellers or privately for a group.
For more detail on your options click on logo or name above.