Marriott is located at the north-east end of Hyde Park at the corner of Oxford Street. It is more 'central' but rooms are nothing fantastic. I thought they would have at least renovated them prior Olympics but alas no. Bathrooms are nice with a very odd shaped bath big enough for two. All rooms have kitchenettes.
Renaissance is to be rebranded as a Marriott. The Marriott sign is already on the top of the building. This property is newer even without the renovations. It is located by The Rocks so lots of happenings, restaurants and galleries.
I think the latter would be a better choice especially if it is on PointsSavers.