I would recommend the RER.
Certainely on a sunday morning, it won't be crowded.
You would have to change lines in Chatelet Les Halles.
If you would take the RER : this will go to La Défense Grande Arche, which is at the far end of the esplanade, looking from the Seine.
I don't know where your hotel is : if it is closer to the Seine, change in Chatelet Les Halles to the metro (I think line 1) and leave the metro in La Défense Esplanade.
enjoy your trip.