TBH as as said both hotels are at the top of their game. However one is more suited to a more mature clientell than the other.

Dont forget that the Sofitel lounge serves 2 small corces from a select menu that can "do" as an evening meal. The Platinum benefit of free breakfast will definatly be useful as the prices in both is at most peoples limit. If you do not have status agree that the STEP rate is extreemly good value ( but you are not paying an advance rate but the best rate of the hotel on the day of booking so can eat into the "profit" as it were. ) Accor Plus also give a 50% discount for 2 people in the rest-urant making it extreemly competative for dining - and if charged to room - I am looking at you Hotel Des Arts - you will get the Accor points