599, I read it like 5 times, it didn't have much dialogue though. The naruto vs pain chapters, I read those about 3 times, it was a good read since it showed the way naruto should have been ever since part 2 started and he looked badass for once and 615, read that one about 4 times.
I don't go back to read old chapters though, I always read the latest chapters from mangapanda and then from *********** since *********** translations are more accurate.