I didn't like my stay in the May Fair, which was admittedly a couple of years ago. Overpriced, small rooms, staff were admittedly quite good, but for £300+ a night they should be. I prefer the PPs which are better value, more light and airy in general, if obviously slightly lower from a star rating perspective.

The PP County Hall and Westminster Bridge are basically next to each other - it's probably only a 15 min walk from there to Horseguard's Parade, basically just across Westminster Bridge, take a right down Whitehall and you're there. PP Riverbank is about 10 mins further away opposite Millbank.

I wouldn't personally stay in Leicester Square. PP Sherlock Holmes is apparently quite nice, not been there myself, but it's in Marylebone and not that handy for either West End or Horseguards Parade. The Grafton is slightly further away still. Mercer Street is in Soho/Covent Garden area, very lively for nightlife but not that close the Horseguard's. Have not stayed in any of that lot.

For my money/points, I'd stay in PP County Hall or Westminster. Walking distance to your Olympic event, plus you're next to London Eye and the whole South Bank area, you can walk up to places like Gabriel's Wharf, nice open-air restaurant area etc.