The Ministry of Agriculture, Forestry and Fisheries publishes regular reports about the tea industry (in Japanese). And the May 2016 report had a breakdown of the tea plant cultivars most common grown in Japan as of 2014.
Yabukita: 75% (31905ha)
Yutaka Midori: 6%
Sayama Kaori: 2%
Kanaya Midori: 1%
Others: 7% (there are some 200 cultivars registered in Japan)
Gabriel, the Saemidori cultivar has been dominating tea competitions in the gyokuro category. I would say that it does so because of richness of umami flavor (in addition to brightness of the green color) rather than being delicate though.
Is there a cultivar considered to be the most delicate, or the highest quality?