Station. Kensington is my favorite area to stay, but there are many other great areas as well. We’ve stayed near the Tower of London near Liverpool Station, which is easy to walk many places. Kensington is amazing for the proximity to many of the museums. Westminster can be very expensive but close proximity to many historical locations.
The fact is as long as you are in the city in a relatively nice area, you can’t go wrong because everything is relatively close.