Earlier this month I used Prestige Transfer (prestige-transfer.com - for some reason there are multiple car services in Paris with the word Prestige in them!) from CDG to DLP and from DLP to central Paris. They were prompt and very professional.
I would've taken the train, but the schedules were very limited with the strike going on right now. Fortunately I traveled between DLP and central London on a Saturday morning so there wasn't much traffic.
I've used ezyshuttle.com as well. They were great. I've also used the RER. It was very handy. Easy to use. I think there were trains every 10 or 15 mins..... You can get a day pass and jump on and off trains and the metro all day. Don't buy the day pass and museum pass grouped together into one pass. It's not worth it.
Sorry... Should have thought of that. My kids are all grown up..... so I just didn't think of that. It's been such a long time. If you have small kids or a push chair. Better off using a car service.