London's Chinatown comprises of Gerrard Street and the surrounding side streets is full of Chinese (and a couple of other oriental) restaurants, and oriental supermarkets etc. There are also illegal Mah Jong gambling basements, money laundering and the hidden influence of the Chinese Triad gangs and the Communist Chinese intelligence agencies.
The restaurants all display their menus outside, so you get what you pay for. Other things being equal, I would choose one which has a decent view of the passing crowds.
Western end of Gerrard Street, corner with Wardour Street.
GPS grid coordinates:
Latitude: (WGS84) N51:30:41 ( 51.511494 )
Longitude: (WGS84) W0:07:55 ( -0.131967 )
N.B. As with all crowded areas in central London, watch out for pickpockets and bag thieves, including the old "distraction" trick, where one member of the gang squirts mayonnaise or tomato ketchup from a MacDonalds sachet etc, onto your clothing and then points this out to you. Whilst helping you clean up the mess, he distracts you enough to allow his accomplices to pick your pocket or bag.
Such gangs are not usually Chinese but are from Latin America etc.