I've been to London several times and stayed in several different neighborhoods.
One that worked out well: Ten years ago, I was traveling with a girlfriend, and we hoped to see live theater as well as go to lots of museums.
We stayed in the
Bloomsbury neighborhood, across the street from a lovely park. This worked really well because it was not far from the Leicester Square theater area, close to Euston Station as well as Russell Square.
It was within walking distance of the British Museum and British Library, and also there was a really good fish and chip shop, the
North Sea, close by. Also nearby was the Camden Market and Regent's Park.
The place where we stayed,
Avalon Hotel, has backpacker-standard rooms as well as "nicer" rooms, but it was not all that fancy.
We always felt safe and secure and we walked all over the place.
Maybe someone else will offer you a completely different scenario--this would give you a different perspective, which is always helpful.