Which Rider series had the best Kaijin designs?
 

Personally, I really liked the Unknowns in Agito. Something about how they made the costumes really made them look organic, and made them feel all the more scary.

I'm actually liking the Zodiarts. The constellation designs work well.
Either them or the Fangire in Kiva.

I always dug the one from Agito as well. They look genuinely scary and realistic to me.

Kuuga had some of my favorites

I have to echo Matrixbeast here - the stained glass look of the Fangire is really good, but I keep finding myself blown away by the ones in Fourze. Especially the Horoscopes.

I love the Fangires in Kiva for their stained glass aesthetic but at the same time I love the variety of designs you get in W.

For me it's pretty much a toss-up between Agito's Lords, Blade's Undead, and Kiva's Fangires. All three of those had a lot of really cool, detailed designs. The Lords might just edge out the other two, but they're all top notch.

The Undead from Blade.

Dopants and Imagins. Zodiarts are alright as well.

them and the zodiarts i think.