I found both the Lanesborough and Dorchester to be disappointing with the latter amongst the most disappointing luxury hotel I have stayed at in the world . The Savoy (pre-Fairmont) was resting on its laurels and Claridges was imperious.
I think One Aldwych is as perfect as it gets. In Covent Garden in the Aldwych, excellent and unpretentious service, outstanding Concierge desk and fitness centre with pool with underwater music.... I think the Four Seasons Canary Wharf comes second.
Oddly, no one has mentioned the Mandarin-Oriental Hyde Park... I am not a "fan" of this place; their top management is arrogant and lacking.