With showa you've got
O.G. (great!), V3 (okay but not that great.), X (Really Really good!), Amazon (short but sweet.), Stronger (awesomely awesome.) Skyrider (melancholic but well-done.), Super-1 (stupider then dirt second half.) Black (awesomely awesome awesomeness.) and black RX (retard made manifested.)
With Heisei you've got
Kuuga(Great!) Agito (even fricken better.) Ryuki (stupider then dirt second half.), Faiz (really good but problematic), Blade (awesomely awesome.) Hibiki (...okay.) Kabuto (Retard once again made manifested.) Den-O (awesomely awesome awesomeness.) Kiva (Evil Beyound recognition.) Decade (short but sweet.) and W (Awesomely awesome awesomeness x2.)
Hard choice but Heisei does have more offenders then defenders so Showa gets the vote.