Drake, because Clock-Up.

Diend is a sneaky one. I think he could pull this off.

First off, G3-x has the best design, but I don't actually know enough about him to vote for him.

So my vote is for Diend. If I'm remembering Decade right then he can summon other secondary riders, so he could technically summon Drake to fight Drake or a bunch of the riders from kabuto to counter Drakes clock up. Plus it would mean he could easily outnumber G3-X.

And Diend complete's finisher is awesome =]

Haha love the Gifs man =p

And yay OOO won =]

diend will just swarm the field with other riders and overwhelm the other 2

G3/X is my favorite of the 3 so I gotta go with him. Simply based on his experience, skill, and tactics I think he could win. Yes Drake has clock-up and Diend has Complete Form but still G3 was a badass in Agito and I still think he is now as well.

Diend would just cloak himself, wait for Drake to Clock Up and take out GX-3. Poor GX is just outclassed by firepower and super powers. Drake would first go toe to toe, then cast off, clock up, and start to take out GX's armor, then Clock over and Rider Shoot. At that time Diend would drop out of cloak, probably use the Trinity Blast (summons Drake and Delta) and hit him with his own Rider Shoot, Delta kick and his own finisher. And just in case, he would probably have also summoned kamen rider Caucasus (he has shown to have no limits in summoning) just in case Drake attempted to clock up again.

Diend wins just for dirty strategy...

Drake.
Before anyone thinks I'm gonna go on a Kabuto rant, hear me out for a bit.

Based on Diend's typical actions and personality, if he's winning a fight but there's nothing for him to gain, he will say something condescending, use Invisible, and run. Maybe summon another rider to distract his opponent.
If he's losing, he'll just cut and run, making liberal use of Invisible's apparent ability to teleport him or something.
Diend's Rider copies are inferior versions to the originals and can be taken out easily, especially for a Rider with Clock Up.

In this fight, there is no arguing that Diend is the strongest. However, you must remember who's fighting. While Drake was never gung-ho for fighting, he would still fight. Diend would only fight if it's in his interest or if it'll mess with Tsukasa's head.
While it could be argued that Diend would fight for the Drake Grip, the Zectors are sentient, so Diend could never use it or get anything for it (And I don't think Diend would really want Drake's make-up collection).

G3-X. He punched God in the face.

Let me say that again.

He fucking punched God. In the face.

G3-X. If you've ever seen Agito, you'll know why.