How to get to...CDG airport...
...the easiest?

Well the easiest way to get to Charles de Gaulle - Roissy airport is probably the solution of a shuttle service or taxi.
You need to reserve your shuttle bus at least 24 hours before your departure day, but it is reasonable to call them at least 48 hours in advance, to make sure there is availability on the bus. You will share the shuttle van with other clients, which makes the shuttle service less expensive than taking a taxi.
...the fastest?
Traffic in and around Paris can be really bad, especially if you need to get to the airport during rush hour, so the fastest way to get to the Roissy airport might be the RER, which takes you from Paris centre to Charles de Gaulle airport 1 and Charles de Gaulle airport 2 - TGV.
Find more information about the
RER B going to CDG Roissy.
...the cheapest?
The cheapest way to get to CDG airport, besides taking the RER is to take a special shuttle bus. When taking the shuttle bus, you can either take the Air France Car or the Roissy Bus. The Roissy Bus, leaving from Opera is less expensive than the Air France Car, which leaves from Etoile or Porte de Maillot.