I have an upcoming stay in July at the Mercer Street property and settled on that after considering it, Bloomsbury, Park Plaza Westminster, PP County Hall, and POTR. All had great ratings on tripadvisor so in the end I went with the Mercer Street because it has by far the best location in terms of being centrally located. I've visited London several times and know location is important and POTRs location isn't ideal with atleast a 15 minute walk to the Tube. It makes walking to destinations not too feasible whereas the two Radisson Blu's I mentioned are within walking distance to loads of sights. I'm also only staying for two nights there (third at a great IHG property) however if I were staying for a longer period of time the space at the POTR would be welcomed.