I've stayed at many Marriotts in London. The two Grosvenor's (House and Square) are nice locations in Westminster, often a bit on the pricier side. Maida Vale is further out and not in as convenient or interesting area. But there are some very good restaurants nearby. Marble Arch is up Edgeware Road and a short walk to Oxford Street. Some good Middle Eastern restaurants. You pay a premium to be in the hub of activity. I'd be interested to hear what others say about the other Marriotts closer to the center of town.
We just returned from JW Grosvenor House (May 1 - 8). It was a very nice facility, a short walk to the Marble Arch tube station and across from Hyde Park. The Mayfair section of London was very nice. We made 3 1/2 day trips (Leeds Castle, Dover, Bath, Windsor, Hampton Courts) as well as all of the London sites using this as our base. It was a perfect trip and the staff was outstanding!! County Hall location looked nice but much more of a tourist area than Mayfair appeared to be.
I have stayed at many Marriotts in London, and I must admit I agree with the person who liked County Hall the best. However, it is also one of the priciest. I found the staff a bit friendlier, perhaps, at the one by Marble Arch. Don't forget the Renaissance hotels in London! I stayed at the one in Holburn last time, and it was a great place. There is a new one near the financial district that just opened this spring...though I haven't stayed there. Regent's Park is a decent location, but when I stayed there the hotel needed some upgrading. It is convenient to the park, to Primrose Hill, and to Camden Town which is an interesting area. No matter where you stay, you can get around in London!
I too have stayed at most of the Marriott's in London. First off, check-out the Insiders previous comments on London. If this is your first time, County Hall may cost you more, but the ease at which you can WALK to so much is well worth the extra cost. Likewise, having a nearby room will help you when the weather changes. Lastly, do the "Big Red Bus", which stops right in front of the Marriott County Hall! Have fun!
A low-key suggestion: one hotel few Insiders (including myself) will have stayed because it only opened 10 weeks ago is the Renaissance St Pancras International. A splendid Grade 1 listed building, the subject of an extensive refurbishment, it might just be worth considering.
Stayed at the Rennaissance, Saint Pancras, last week. New hotel, just had their grand opening. Very nice rooms, executive lounge is great as well as restaraun. Staff was very attentive. Located next to Kings Cross train station. Definitely recommend. Hope this helps, safe travel.
You know, I think the others have given you valuable advice. The Marriott County Hall can be pricey, but if you can get in there, do it. I stayed in that hotel the first time I was in London and it was great. I have stayed in a few other Marriotts in London, but I didn't like any as well as I liked County Hall. However, the one in Kensington is across from laundrymats, supermarkets and not too far from two tube stations. The Marble Arch Marriott is in a Middle Eastern part of London, but not far from Oxford Street and the busses connect you well to the tube. Check out the London Pass for attractions. The Oyster card is used for transport, there is a 5 pound deposit and then it deducts fares to a daily maximum. You can get the Oyster card with transport if you wish. Ask if you need to know how to get downtown. Have a great trip.
A lower cost option is the Marriott West Quay, doesn't compromise on the luxury and has transportation within 2 minute walk (Jubilee Underground (Metro/Tube) and Docklands Light Railway) can take you to the centre in 10-15 minutes. Try the Imperial War Museum (Lambeth North Tube station) its free. Try the Borough Market for the hussle and bussle of a cosmopolitan market and lunch (London Bridge/Borough Tube) Try to gain access to the Ceremony of the Keys at the Tower of London in the evening - this happens every evening and has done so for hundreds of years without fail - including during WWII. Have a beer in the Punch and Judy pub in Covent Garden (Leicester Square Tube) whilst watching the street arts entertainment - great in the evenings. Leeds Castle in Kent is well worth a visit - one of perhaps the best castles in England, similarly Hever Castle in Kent. Both about 1 hour from London Hampton Court Palace in Surrey is awesome and steeped in the best history of Henry VIII. Try Pie and Mash (with Liquor - parsley sauce and chilli vinegar ) at the Angel market or opposite the Old Vic theatre for tradional food. (waterloo tube) Have a great trip and I hope this helps others!