For me and since I did most of my stays at Marriott, I put the comparison between Accor and Marriott brands
Fairmont : Upscale luxury hotel , similar to The Ritz-Carlton of Bonvoy
Raffles : Upscale luxury that supposedly provide personalised experience. I would put Raffles as competitor for St. Regis even though St Regis will be less personalised due to the size of the hotel.
Banyan Tree : I havent tried this before, so no comment but I always think they should be close to Aman style resorts.
Sofitel Legend : Another Raffles type of hotel .... Those luxury hotel with their own story to tell ....
SO/ Sofitel : Mixture of the classic presentation of St Regis with the youthful atmosphere of W Hotel (based on my stay at So/Singapore)
Sofitel : luxury business hotel ... similar to JW Marriott/Westin
M Gallery : Toned down version of Marriott Luxury Collection hotels.
Pullman, Swissotel : The Marriotts of Accor .... supposedly upscale business hotel but unfortunately brand standards is pretty hit and miss.
Grand Mercure,Mercures : The Sheratons of Accor .... again mixed standard ... can have a good Mercures and bad Mercures all in 1 country.
Novotel : to be honest I'm quite confused with this brand. Do they supposedly better than Mercures ? but some Novotels are better than Mercures and some are worse. Similar to Courtyards/ Four Points of Marriott
Ibis : Cheap but supposedly decent for its price (especially Styles) Aloft and Moxies of Accor