My pick has got to Kurama vs Karasu. I saw so many responses for @VinMcCarthy card so I had to get in on the fun!
I remember how nervous he was for this fight and for good reason. We were unable to see Karasu's attacks so there wasn't a good strategy to defeat him. There's a moment when they meet before the fight and Karasu has Kurama shaking in his boots and delivers the line "bang" as a reference to his explosive abilities. And as the fight went on, Karasu was just kicking his ass until Kurama's trump card kicked in. An elixir given to him from a former opponent which would bring out his true form, Yoko.
And my God....you show me someone who didn't swoon for Yoko Kurama, I'll show you a gotdamn liar!
The tables quickly turned and then Kurama has Karasu trembling in fear and gets him back with his own line "bang" as seen above which is probably my favorite line/moment in anime history.