CDG Hilton
Haven't stayed at the CDG but just got back from the Hilton Arc de Triumph. Based on how far away that hotel is, even with the train, I would not stay there. The RER train has some pretty shifty people on there.
FYI- There is also the Hilton Eifel and the Hilton La Defense which are closer in.
Everytime we rode the RER to anywhere it wasn't pleasant. Just my opinion.