I don't know what the best fighting scene was, but I do have a short list of favorites:
Daniel LaRusso vs. Chozen The Karate Kid Part II
Leroy Green vs. Sho'Nuff Berry Gordy's "The Last Dragon"
Rocky Balboa vs. Apollo Creed II Rocky II
Rocky Balboa vs. Clubber Lang II Rocky III
Bruce Lee vs Chuck Norris The Way of the Dragon
I'm waiting to add Luke Hobbs and Deckard Shaw vs. Brixton Lore (aka "Black Superman") in Hobbs & Shaw