Well, I liked the scene where Ichigo fights Kenpachi [I think that's episode 40+ or something, not sure] and also the betrayal of Tousen plus Ichimaru Gin and Aizen, when three of them fly to the sky. That was cool, every captain was looking at them hopelessly.
The fight scenes between Renji and Ichigo, Renji's power and also the one with Ichigo and the captain-brother-of-Rukia, Byakuya. Like the faces they made when they fight! Byakuya's bankai, unforgetable.
I wouldn't say best, but these were good episodes. When the Anime will be finsihed I will tell you the best one.