If we assume it's in JAPAN, then Oda. But if not then probably Emiya, though Oda is still very powerful servant

But would Nobunaga be able to affect EMIYA? Nobunaga's Noble Phantasm is specialized for battles against Divine Servants, which EMIYA is not. And since EMIYA is a modern Servant, Nobunaga's skill also shouldn't work to a significant extent.

Oh right, kinda forgot about that part

Yeah, with Demon King of the Sixth Heaven and Unifying the Nation by Force both being powered by the Mystery and Divinity of a target EMIYA is an unfun opponent for Nobu. Even Three Line formation wouldn't do much since it scales off of Unifying the Nation and the target having Riding, which EMIYA doesn't.

Emiya is her worst possible opponent. He outclasses her physically and skill wise so he dominates in close quarters, his own spam can counter hers, he has more one shot options, and literally none of her buffs trigger against him, which also means that in a clash of reality marbles it'd be UBW's A++ to DKotSH's E-C at best.