Beware the location of the Regent's Park Marriott. Although it's only a short walk from the Swiss Cottage tube, that line (Jubilee, I think) doesn't go to Oxford or Picadilly Circus, requiring a transfer. Unlike New York, the Underground does not run late at night so if you attend the theatre, followed by dinner, followed by a club, you'll find yourself taking a taxi way out to the Marriott. And the hotel is 1970's ugly modern. As long as you're not paying, go for the Grovsnor Square (I am redeeming 5 nights there in October and I can't wait!)