Love the PL. Stayed there during the Olympics. There were three of us, including our (at the time) 17-year-old son, and we were fine sharing a room. Excellent concierge lounge, very good service, extremely close to the tube, walking distance to a great deal. I would stay there over MV unless you really don't have the points.

If this is a rare visit to London, the time you save on transport is worth so much more than the points. You can always earn more points, but unless you visit London frequently, you will not be able to replace the minutes you waste getting to where you are going. A little time saved here and there may mean a few more sights seen, or an additional show or museum visit.