If we're talking canon then yes, D'dore v. Voldemort in the Atrium is the best by far. Still, Snape v. McGonagall, Slughorn and, IIRC, Sprout near the end of DH is hands-down the second best.

If pressed, I'd pick either Snape's wtfpwnage of Harry at the end of HBP, or Harry's carving Draco like a thanksgiving turkey as the third most enjoyable, though not forthe same reasons.

Of course, D'dore's pimp-slapping of Fudge et al in OotP was also :awesome

 

^There's a bang and then everyone's unconscious. Made me lol.

 

I enjoyed all the fight scenes in the books. J.K.R has a talent for writing action, which is why I found it surprising that she didn't do more of it in the books.

As for exemplary duels in fanfics, I personally feel that IP82's Potter's Resistance featured one of the best duels that I'd ever read in fanfic. The Harry and Rookwood fight was exactly as a wizardly duel should be.

Also, my own story ASHH and my one-shot Tequila features some duelling scenes, feel free to take a look.

 

Could you link to that fight? I tried to read the story but I made it part-way through chapter 2 and currently want to stab something.

 

Here you go.

It's in the middle of the chapter.