I stayed at Westin Paris for my last few trips to Paris and took the Roissybus to/from CDG. It is walkable from hotel to Opera with light luggages. Roissybus is not very comfortable, but I am ok for the ~50 min ride. It is 9.40 Euro, every 15 min during the regular hours.

Air France bus is not convenient for the Vendome location, need a transfer at Porte Maillot to go to Westin/Hayatt. Last time I used it to go to LM E'toile, it was a long wait and I heard it is less frequent now (30 min?). One way is 15 Euro, but more comfortable.

RER is my least favorite choice, it can get quite crowded (no seats) so need to watch out for belongings. RER works out well for some locations (i.e. Hilton Paris, now is a Pullman). It is a long walk to transfer to metro at Châtelet-Les-Halles for the Vendome location.