Even though they are nostalgic, the worst would have to be between Riderman, Ichigo and Nigo, original Spiderman and the Rinoserous man.
Most of the old Kamen Rider outfits just looked like sweat cloths with breast plates and a helmet.
A lot of people don't like Decades costume, but I would have to say it is better done, the reason why is, because unlike a lot of the Kamen Rider series from the Heisei era, you don't see the opening in the back of his costume, and it is sleek fits right, and flashy, so it fits his character.