I'm going to throw in my vote for the Maida Vale property as I have yet to cough up the money or points for County Hall or Chancery Court. I stayed at the Maida Vale in February for a week, and I was struck by the extraordinary service, particularly the affable bar keep, and the recent renovations are quite smart. I paid with points, and the Maida Vale is the only Category 5 hotel in London proper, which amounted to a significant point savings. Although it is a bit further out, it is a two minute walk from the Kilburn Park tube stop as Cornroaster mentioned in an earlier post, and only three stops from Paddington Station where the Heathrow Express drops you off. As for the safety of the neighborhood, I was out well past Cornroaster's 11pm bedtime (I was with my friends in their early 20s) and never felt threatened.
Although I have never stayed at County Hall, I would consider spending the money on my next trip in January for two reasons. 1) The view can't be beat. 2) The County Hall is home to, in my opinion, the greatest bar in the world: Shino's. It's located on the embankment near the Dali museum, and has relatively cheap beer and fantastic jazz. Highly recommended.