Kuuga.
Birth can't even handle a complete Greed.

Most powerful Rider ever vs. coin op Iron Man? This isn't even fair.

I like Birth a lot (Date more than Brotou, of course, but both are cool), but there is nothing he can do that Kuuga can't shut down easily. Various arms? Titan form can tank that. Take to the air with Cutter Wing? Pegasus form is made for that. Breast Cannon? Good luck keeping Dragon form in place long enough to aim and fire. Yusuke's got this one without even needing to touch the Rising forms.

Poor Birth. I love you, but you're pretty much outclassed in every single way.

I like Birth and all. But on what planet, in what alternate reality, using what handheld Nuke does he beat Kuuga?

Well, seeing how one sided it is right now, if Kuuga gets 10 votes before Birth gets 1, I'll close this battle early (poor Gotou, the random number generator was not kind to him)

I know right? Man had no chance against Kuuga.

Seriously, when I was using the thing I was like, "okay, OOO vs Double, Amazon vs Super-1, Kuuga vs...oh...oh shit..."

I share this opinion 100% Kuuga just flatout outclasses Birth. Without his Cell Medals, he's powerless.

Birth Self-Destruct system?

Gotou disabled it already, remember? :lol