with the road construction around the airport, I would stick with the trains. one watch out- when I was there in late March, the RER from Gare du Nord to CDG has a limited run in the pm- ie, the direct to CDG train doesn't run after a certain hour in the later evening. you apparently had to get off at the branch (sorry, forgot its name) and find the bus... another data point: took the roissy bus to the Opera just to try- 2+ hrs in stop start traffic (mid day) which is way too much stress coming off a TALT flight-even in J... and due to terminal construction, the pickup was waaayy around the other terminal (whatever the terminal is that is on the other side of the Sheraton walkway)