I love Tempura. Maybe it should be written like Tenpura in correct transcript from Japanese translation. Not a big deal with it, though.
In Tokyo, we find several top Tempura restaurants when walking in such big stations as Shinjuku, Ginza, Ikebukuro, Shibuya, etc.. Among them, maybe the most recommended for avarage people is either Tsunahachi or Tenichi. Both are really fantastic for me. But if I dare to judge which is better, I would have to choose Tenichi. If you go to Tsunahachi, I promise that you can have splendid Tempura dish experience. However, Tenichi could be the top in my ranking.
Reason for the decision is not that hard, it's just my taste. Actually I just love both of the restaurants. Just a little taste difference is that Tenichi's tempura is a little crispy ( just a little ) and fired flavor is a little stands out. Tsunahachi's tempura is fried a little softer than Tenichi. This is my impression, I'm not sure if you all have the same opinion about the two shops.
If you ever come to Japan, or if you are already in Japan, excellent tempura dish should not be missed. I've tried tempura overseas, but unfortunately, most of the casual restaurants' tempura in foreign countries are not the tempura at all.
Please try the real one in Japan.
I had Tenichi Tempura in Ikebukuro. There are nice restaurants on the top floor of Seibu department store in Ikebukuro, also on the top of the Parco building. Both are popular and located just at the JR station exit.