[Matrixbeast]

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).