Radisson Blu Mercer Street - hands down. I've stayed at a few and this location is the best, lively during the day (right at seven dials in Covent Garden) but pretty quiet at night. Excellent options all around for coffee (Monmouth coffee is a must, Hotel Chocolat), eats (avoid the touristy stuff like Jamie Olivers - try many of the great smaller wine and tapas cafe's), shopping (Oxford madness is 15 minute walk, boutiques on your doorstep). Tube, Soho, theatres, Trafalgar square all 5 minute walk. Very attentive staff, good (small) gym, decent and free wi-fi. We actually spent a fair amount of time in the Covent Garden Hotel's lounge pre-dinner right next door - pricey but great cocktails and appy's. ^