I'd suggest that you initially take somewhere cheap, on short lease and as central as you can afford whilst you get a feel for living in London.
Then take the time to explore different areas, sort out some work and find an area you'd be happy to "settle" for a while. When you first move to London you probably want to be making the most of the nightlife, seeing everywhere and not worrying too much if you live in a tiny dingy shoebox - there'll be other things you'd rather spend the money on.
You just don't know where you are when you move here first....
