My favorites in no particular order, I love them all for different reasons are:

The Atheneaum on Picadilly
The Ritz on Picadilly
Mandarin Hyde Park
Renaissance Chancery Court - This is the quietest London Hotel ever
The Langham (formerly Langham Hilton)
The Goring - Like staying at a friend home. Very quiet also
Threadneedles (in the City)
Marriot West India Quay (Canary Wharf)

All have excellent service, rooms and great concierges....
Will be back in London in March and staying at Canary Wharf again. I love the City and Canary Wharf though most tourists find them a bit off the tourist track.