ClementDu,
I want to change my answer. If you plan to be staying in the northern part of Tokyo, it may be better to land at Narita Airport. You may be able to get a direct train to, say, Shinjuku Station (on the N'EX Train) from Narita Airport, which would not require changing trains. Haneda Airport is much closer to Central Tokyo, but you might have to change trains 2 or 3 times to get to your destination in Tokyo, and changing trains in Tokyo might be a bit of a challenge for you. Where do you plan to stay in Tokyo?