I'm not just saying this because it is recent, but IMO the Luffy vs Katakuri clash was the best for a couple reasons.
1. It showed the raw power of Kings Haki, without having to have physical contact, unlike the clashes with Luffy vs Chinjoa, Doffy, and Big Mom. The effect on the environment just by unleashing it was insane.
2. They were not using it to attack each other, but instead using it the ensure that no one else interrupted their fight. Which was a clever was to reveal that Katakuri also had it.
3. It focused more on the Haki itself and not on an attack, so you go to see the actual aura of their individual haki mixing, and how overwhelming it was.
Doffy and Luffy's clash was simply a clash of King's which I mentioned before, we had seen multiple times before during that arc