I'd definitely pick Tokyo!
Not just because it's huge either.
I hosted a Japanese Exchange student a few years ago durring my senior year of high school. He's now attending Sophia University in Tokyo.
Sophia University happens to be a sister school to the college I'll be graduating from next spring, Penn State University. And from my limited experience of traveling abroad... The bigger the cities you go to, the more English they know
I studied a bit of Japanese back in high school for 4 years. Since I go to a small satelite campus of Penn State I don't have the opportunity to take Japanese or even test out of foreign language credits. So I've gotten quite rusty, not that I had much knowledge to retain >.>
Anyways, Totally Tokyo, Hands Down!