Well, I've got favorites from the 80s, 90s, and 2000s.
I guess if I was to pick a favorite, then I would pretty much just go by which decade had the most seasons I liked. For me, that would be the 90s. I enjoyed 8/10 of it's seasons (Jet, Dai, Kaku, Oh, Car, Mega, Ginga, and GoGoFive).
I loved 5/10 from the 80s. The second half basically (Change, Flash, Mask, Live, and Turbo). And I loved 7/10 of the seasons from the 2000s (Time, Gao, Aba, Deka, Magi, Bouken, and Geki).
So yeah, I guess 90s wins for me. hahaha.