What's so funny about those decades? Just off the top of my head the 70s saw the start of Jan Svankmajer's career, Ralph Bakshi shaking up Hollywood animation, arguably a golden age for British kids' TV, some early work from Caroline Leaf, about half of Kihachiro Kawamoto's shorts and most of Yuri Norstein's films.
And the 80s had the start of Channel 4's reinvigoration of independent British animation (with Nick Park's career starting at the end of the decade), beginnings of the Disney renaissance, the release of a good portion of the Brothers Quay's filmography and some classics from Studio Ghibli. Both decades are good contenders if you ask me, the 80s in particular.