Kabuto, high diff.

Funny obito solos

Obito mid-high diff

Without Edo Tensei. Kabuto has no way of countering Kamui (even with it he’d need someone crazy fast), and OM Obito should have better stats than White Mask Obito since he doesn’t have the Rinnegan as a massive chakra drain, so he should be as fast as KCM Naruto at MINIMUM

Plus Obito’s genjutsu is Kotoamatsukame level, so he could just use that. It worked for decades on a perfect Jinchuriki, Kabuto isn’t breaking it.

I'll try and give a more in-depth point of view of what I think later, but I'm leaning toward Obito right now.

Obito (high diff)

Kamui grants almost complete invulnerability.

Kabuto extreme diff .

Kabuto mid diff