Depends in which Terminal you're landing. From T1, you can take a shuttle train. From T2, you can walk.

The Air France bus is only a bit more expensive. It's easier if you're landing at T1 and the whole ticketing system is more straightforward. Less walking is involved as it stops right outside both terminals.

I used to work at CDG and our supervisors recommended that we take the Air France bus instead of the RER. More secure and less chance of getting pick pocketed. They had 3 F/A's "lose" their passports on the RER and sure enough, a few months later, a coworker couldn't work the trip when she looked in her bag...

http://videocdn.airfrance.com/cars-a.../index_en.html

Everyone on board is going to and from the airport. It doesn't stop in between to pick up or drop off anyone. They also do the route all day so if there is bad traffic, they radio each other and take alternate routes. The only time it was ever late was when we were actually blocked by a truck...

Taxis are usually lined up where the bus stops so that was never an issue, or you can continue by Métro. So pick the stop that's closest.

If you opt to take the RER, secure your money and passport (the Real Prize for pickpockets who sell them on the black market). Rip the tags off your bags before you board and don't fall asleep! Easy to do if you're landing after a transatlantic...

Have a good time!