What is the best (free) museum in London?

It depends what kind of museum you are interested in.

All the major museums are free as they are government-run for the benefit of the public (though they appreciate a donation!) The British Museum (nearest tube Tottenham Court Road) is full of ancient antiquities, Greek, Egyptian, Roman and more, and there is a whole cluster of national museums very close to South Kensington tube as a legacy of the Great Exhibition of 1851 - the Natural History Museum (dinosaurs and anything to do with biology, and the building itself is a beautiful example of terracotta architecture), the Science Museum (all other kinds of science), the Geological Museum (anything to do with geology, rocks, earthquakes etc) and the Victoria and Albert Museum (art, architecture - impossible to describe in a few words).

If you're thinking of art museums, try the National Gallery and National Portrait Gallery in Trafalgar Square (nearest tube Charing Cross) and the Tate Gallery, now split into Tate Britain (nearest tube Pimlico) and Tate Modern (housed in, of all places, a former electric power station on the south bank of the River Thames! nearest stations Southwark or Blackfriars).

The British Museum (tube is Tottenham Court Road - Central and Northern lines) is Absolutely massive. You will need several days to do everything! They also do free talks about some of the rooms that last about half an hour. There are rooms on just about anywhere in the world and totally fascinating. Although entry is free, eat before you go in as food is very expensive. Photography is permitted in all areas of the museum (except the reading room which is the only place that does have an entry charge).

http://www.britishmuseum.org/

On the link below Tate Britain Museum has been voted best free museum in London.

Best Free Museum in London: http://gothisplace.com/Search/English/best%20free%...

On a separate note GoThisPlace.com can be used to search for many Natural Language queries like ‘Best Free Museum in London’, this is due to it using a system called Geo Text Search which tries to understand and then answer your request just like another human being would.

They're all free, but will I like the Science museum, the Natural history museum is best.

Depends what you are interested in. If you want to see dinosaur skeletons and animatronics go to the Natural History Museum (tube = South Kensington). If you want to know about the history of London go to the Museum of London (tube = Barbican). If you want to see old toys and games go to the Museum of Childhood in Bethnal Green. The Science Museum also in South Kensington has history of aviation, earthquake zone etc.

They're all good.

as well as those listed above, you also have the imperial war museum which is also free and pretty interesting