Of the London properties I've stayed at, this is how I would rank them (highest first, and also number of minutes' walk to nearest tube):
Grosvenor House (3 stays) - 6-7 minutes
Chancery Court (1 stay) - 1 minute
Marble Arch (1 stay) - 4-5 minutes
Kensington (3 stays) - 4-5 minutes