Best to Travel in London by Bus or Tube?

Depends where in London you are going and at what time. Tube is generally the easiest of the two, although walking is funny enough very easy around the centre. Buses are more useful late at night or if you have a specific route. Once out of the centre the tube is available more in some areas and less in others. I come from the SE of London and buses were the only way to travel around. Do you have a specific area or places you wish to visit?

Metro is quicker but it's all subjective depending on where you're going to and from.

Most of the main tourist places are fairly close together you could just walk. The tube is faster, but you could also travel on the open top tourist buses, which will also help to give a sense of the layout of the city. Don't get a tube between Piccadilly Circus and Leicester Square, they are really close together and it's faster to walk.