Depends what is important to you - the OP mentions that the gym at the Montparnasse was not up to scratch (from memory it is just a normal guest room that they have stuck a couple of machines in). If a gym is important to you then the Etoile may not be the one for you - I was there a couple of weeks ago and on checking out the person next to me was complaining about the gym (it is a 3rd party gym across the street) and the fact that it cost €25 per visit (from recollection).

The LM Etoile was adequate for my needs, across the street from the Congres for the conference I was attending, on Metro line 1 to visit La Defense to see some clients and close to Neuilly sur Seine for my local office. Room was distinctly average but had good broadband in the room (about €20 per day). Didn't use any of the bars and restaurants so can't comment on those - had some colleagues staying at the Concorde LaFayette oppostite so we ended up in the rooftop cocktail lounge there a couple of nights - asking for the bill is not for the faint-hearted at €23.50 per person for the first drink and €11 pp thereafter, great view of the Eiffel Tower though.

Having said that, comparing my previous 1 experience at LM Montparnasse with LM Etoile, the Etoile is a couple of notches above the Montparnasse! (it would be difficult to be as bad as the Montparnasse!)

The PdG in Av. George V is a top hotel, certainly would be my choice if you can get a good rate. If you do stay at the PdG then there is a great restaurant opposite called Flora. The PdG is much more centrally situated for the sites if you are doing touristy things. It is less of a business hotel as suits the Luxury Collection tag - much more interested in ensuring your comfort. Can't remember what the situation is with a gym there.

Can't comment on the Westin at all, not having stayed there.