Yep, as volajuv said the first two are better -I suggest to watch the 3rd too, just to complete the series.
Speakin of completin the series, though, take note that in 2005 Miike Takashi filmed a "remake" of the first one,
Yôkai Daisensô, with the same title by the way. It's kinda different from the 1968 version, and it's also different from usual Miike movies, but it's enjoyable. I would say it's more of a fantasy film then an horror one.
Produced by Kadokawa, it was, at the time, one of the biggest productions from Japan [in terms of budget]. This was something new for Miike, as he usually work[ed] with low budgets, but you see where the money ended
And there's Sugawara Bunta in it, as the granpa. He was good as he always is. On the girls' side, Chiaki Kuriyama. Nice as always
All in all, I suggest to watch the 3 original movies,
and the Miike one. The originals because if you love old japanese movies from those years, you'll like these too, and the 2005 one because, well, because it's Miike we're talkin about. Genius at work in my humble opinion.
