It's easy to catch a Taxi at CDG. Inquire before you get in the car about the cost. They shouldn't quote you more than about 60-65€. Have the actual address of the hotel on hand for him/her, 70 Avenue des Champs-Élysées. You can arrange a car service too through the hotel in advance. jerrycoin can tell you how.
What you may want to consider nan061 is to email the concierge at C-E, and get a price on having you picked up at CDG. It usually runs the same price as a taxi, but you will have someone waiting for you as soon as you clear customs. You won't have to find a taxi, wait in line, and it is so much more relaxing. After a long flight consider letting someone else "Do your thinking"!
If you need more help, let us on MRI know, and we will try to help!
Lastly, please make sure you review previous Parisian Posts to determine how you want to spend your time in Paris!
Seriously, don't drive... Both for driving and parking. Like many old cities the roads are totally inadequate for the traffic, so the metro may be your best bet.
CDG is built directly above the rail station, simply take the RER B to Chatelet and then line 1 metro to Franklin D Roosevelt which is only a few stops. As you leave follow signs to the Champs Élysées exit and when you get there take the left staircase, walk straight out as you reach ground level and you're on the Champs Élysées, the Marriott is a few minute walk on your right. Whole journey from CDG to hotel takes about 30/40 mins.
I do like the Champs Élysées Marriott and have fond memories of my weekend there a couple of years ago, upgraded to a 3 floor suite overlooking the Champs Élysées... Wow!
Likewise, one should buy a Metro Pass at CDG, for the length of time they are going to be in Paris. This will get one off to a good start. The RER starts at CDG, so it makes it easy for people to take it, save some money, and travel around Paris.
Once one gets to The C-E, the "Hop on/off Bus" is the way to go! You can take these to three different zones throughout Paris.
I agree that driving in Paris is completely unnecessary and a waste of money. I'm a public transportation affecionado myself, never choosing to spend coin on a taxi (either) from an airport unless it's absolutely necessary (or the rare mood strikes). It's just a personal choice, which has to do with why I travel (mostly for cultural and historical exploration and adventure as opposed to romance and relaxation), environment conservation and also how I choose to spend my budget. People talk about how the scenery isn't exciting when training from the likes of say LHR into London or CDG into Paris, but I find just about anything foreign interesting if I haven't seen it before. The RERB line from CDG into Paris maps through some less affluent suburbs that are rather rundown, but then you get to see how people live.
DO NOT EVEN TRY TO DRIVE IN PARIS!!! I speak from personal experience. First of all, it's just plain dangerous. But more importantly, especially if you rent your car at CDG, you're going to have trouble getting to and from the airport. My one and only time renting in CDG I ended up en route to Lille. (A kindly toll booth person directed me back so I could head toward the Loire Valley.) Coming back was a nightmare beyond belief. The signs on the Boulévard Périphérique are quick -- usually you see them just before you pass them -- and they often seem to point in conflicting directions.
My one horrific experience returning that car was using up 4 tanks of gas and as many stops at gas stations on the Boulévard. I simply could not find the exit. (It doesn't help that there is an interior and exterior BP.) At one point I took a wrong exit and ended up in Paris. The only good thing is I know to rent a very compact car in Paris. It was harrowing.
What Pluto says is correct. The RER (very inexpensive) is safe and fast -- and as long as you get a direct train to the Gare du Nord) despite traversing through some of the most poverty stricken suburbs of Paris. I would never, ever rent a car at CDG again, even though when I returned my car after that bad trip back 4 hours late they were very nice at the airport and didn't charge me extra.
The trains in France are probably the best in Europe in speed and reliability (esp the TGVs). When I researched my Joan of Arc book I had to rent a car but did so in Angers for the Loire and Nancy for the area around Domremy. Also, as probably has been mentioned (I have not read the whole thread), if you cannot drive a stick shift, reserve in advance AND CONFIRM. Even some cars are bi -- the one at CDG was and the previous driver had left it in manual. I cannot drive a stick shift, and the woman at the outside kiosk couldn't do automatic so she had to call for someone from inside to help. It turned out to be fairly simple, but not obvious because of the difference in vowel abbreviations.
Bonne chance -- and take the train!
PS -- I now read the whole post. It doesn't seem like you were planning to rent a car. Let's put it this way in terms of having a car pickup by the hotel or taking the RER: money. If money is no consideration, be picked up. But the RER has excellent service unless you have lots and lots of luggage. There is also an Air France bus that drops off at a couple of locations -- although I never stay in the Champs-Elysées area -- I think it also goes to Denfert-Rochereau. I suspect CE would be near or at one of those stops.
We took a bus from CDG to the arc de triomphe and then walked a short bit down to the hotel. Was pretty cheap, crazy easy and made for quite the "welcome to Paris" as we just sorta took it all in walking down the road to the hotel.
Now if you have a lot of bags, taxi/car service is better. We traveled with single carry on each and a backpack for me so luggage hauling down the road wasn't hard to manage. The return trip we took a cab to the train station and then took the train back out to CDG. It was actually about as easy as the bus just required a bit more planning for timing the trains. The bus as I recall just runs fairly regularly
a couple of years ago I wanted to take the bus to the arc and then walk but we waited say 30 minutes and either were in the wrong place or just wasn't that frequent so we took taxi and last time we just took taxis more expensive but very convenient. and the Champ is a very busy road( sidewalk) like 5th ave so walking with luggage can be a challenge