Probably need to examine your criteria, for example, location, comfort/luxuriousness of room, hotel facilities, cost
my take on these (and in the order I prefer them in each category...)
Location
Westin fantastic location, good for Louvre, Boulevard Haussemann for shopping, also on metro line 1 - prefer this location for most things over PdG.
PdG location good for sight-seeing (Champs d'Elysée, Arc de Triomphe, Eiffel Tower, Louvre etc), on metro line 1 so you can easily get out to La Defense if you need to for business.
Le Meridien Etoile - good location for business, air france bus from CdG/Orly stops outside hotel. on a couple of metro lines. not great for tourism as a little bit on the outskirts of the centre.
Sheraton CdG -personally I try not to stay at airport hotels unless I am arriving late, leaving early or have a meeting there. Generally I take the Eurostar to Paris (or Thalys if coming from Brussels/Holland) so don't tend to go to CdG.
Le Meridien Montparnasse - err good if you are arriving at the station. grotty nasty location otherwise.
Comfort/Facilities
PdG - luxury is the word that sums it up, very elegant and a little understated. The only one of the hotels that it isn't sometimes a lottery about whether you get a refurbished room or not, always very nice!
Sheraton CdG - fit for purpose!
Le Meridien Etoile - functional business hotel, does what it says on the tin though avoid some of the smaller non-refurbished rooms looking inwards onto the inner courtyard.
Westin - sometimes up there with the PdG but until the refurb is complete there is always the chance of getting something quite grotty
Le Meridien Montparnasse - do they still make orange/brown swirly carpets or were they a special order?
Cost
LM Montparnasse - funnily enough it is quite easy to get a good rate at this establishment - I'd pay €100 (or less if possible)
LM Etoile - huge hotel so usually availability though can get pricey when there is a big convention on at the centre opposite. Pay €100-€200
Westin - can usually get a rate in the €175-€250 range
Sheraton CdG - seems to normally come up at around €200
PdG - you have to pay for the best things in life, usually seems to be €300 or more a night...
Overall I think the Westin wins :-: