I really enjoyed watching 火影忍者 vs Pain. It made me sad and happy at the same time, and Hinata finally confessed wich made happy since I'm a huge Naru Hina 粉丝 (maybe there will be some NaruHina in the future) and all in all the fight was epic :)
My 最喜爱的 fights are probably from Ninja Scroll TV series. I 爱情 all the bizarre creatures and artistic violence. 最喜爱的 particular fight is probably the first main one where the village gets wiped out, it just sets the mood for the rest of the fights in the series. Don't have a video of that particular fight, but here's an AMV with many fights. Pretty bloody stuff.