For 7 days in one location, I would choose Paris by far. 4 days in the city and Versailles, Normandy, Loire valley or givenchy day trips based on your interests.
I prefer the renaissance hotels in Paris, the Marriott has an A+ location but The renaissance hotels feel more local.
London has a number of great hotels (JW, Park Lane, Edition - no lounge though) and Rome (Exedra or grand flora) are other decent options. 7 days in once city in Spain is a lot, Spain is better as a multi-city run.