JRA-25 is the older version of Japanese reanalysis. It has lower spatial resolution and some deficiencies (https://www.jstage.jst.go.jp/article/jmsj/93/1/93_2015-001/_article). JRA-55 is much more reliable except you want to do a comparison/sensitivity study.
I usually download JRA product from its main page in http://jra.kishou.go.jp/JRA-55/index_en.html.