These are the choices one really loves to make!
Two VERY fine properties!
Both are smallish and VERY "classy" as well as being included in the Amex FHR program and you can get a free afternoon tea as such!
I'd say it's a location thing primarily- yet they are not far from each other! The Bristol was just remodeled last year or the year before and with about 150 rooms or so is about twice the size of the Imperial, which I believe still serves as a kind of official residence for visiting dignitaries/officials!
Ever so very slight nod perhaps to the Bristol!
Enjoy!