I'm posting in c/movies but including tv shows, anime, comics, manga, etc.
Personally I think the final war rig sequence in Mad Max: Fury Road is the most impressive live-action fight I've ever seen. The practical effects and choreographing are incredible and the fight keeps moving along by having the stakes raised and characters dying, it doesn't meander.
In animation it's harder to say. Attack on Titan had a lot of really well animated action (it used be so good, goddammit). The battle in Shiganshina in season 3 is the best, the narrative weight is so strong, the characters all have really good moments, the stakes are really high and the production is incredible, animation, soundtrack, sound design, voice acting etc.
Mob Psycho has the most consistently incredible animation of anything I've ever seen, I think the group fight against the teleporting psychic in season 2 is my personal favourite, even if it's not the flashiest, it's really well directed and just such a cool fight, even though it's not that long.
The ChainsawMan manga has a lot of good fights, the Falling Devil arc is like my favourite arc of anything ever, but that's mainly because of the characters. The art is stunning, Fujimoto at his absolute peak, but the action is pretty straightforward. I mainly love it because it's Asa at her best as a character, and Asa is my favourite character of anything ever.
Wow it was way easier for me to choose a live action sequence than animated. Honestly there's so much lazy action in superhero slop that Mad Max stands out so, so much.
. The guy riding against and right through a Japanese cavalry formation with his lever-action is just 
