For me it is Saitama vs Boros. As the reason, you know because that scene when fists collided with each other is truly exciting.
Madara vs Shinobi alliance It never fails to amuse me whenever Madara kicks the Shinobi alliance's but.
Hellsing Ultimate - Seras Victoria vs Zorin Blitz, tho her later fights with Captain and Major were great too.
Gundam 00 Allelujah/hallelujah vs Soma Pieries/Lieutenant Colonel Sergei Evangelion 2.22 Shinji/Unit01 vs Zeruel fate/zero Gilgamesh vs Berserker a certain scientific railgun Accelerator vs Dark Matter Fate/Stay Night most of Archer's fights Gundam Iron blood Orphan Season 2 Final Fight
I tried to tag a few fight scenes, but all I ended up doing is watching and thinking about 100 other fights. There are just to many. So sorry can’t choose one.
I wouldn't really say I have a favorite so I will list a few of the ones I enjoyed the most: Netero vs Meruem (Meruem playing against Komugi is epic too somehow) Eren's first transformation and his fight against the female titan in the city Kirito vs The Gleam Eyes Basically the entirety of Bleach (Bleach is far from my favorite anime but I really like the fights) I can't really remember much other than these from the top of my head
Sword of the Stranger final fight scene Hamatora episode 1 fight (it isn't for a long duration, but it was nice)
If you haven't seen JJBA Stardust Crusader, you haven't seen true (anime) beating Bad asses ladies SUPERMARKET BARGAIN DAY!!!!!