This Naruto and Sasuke's battle at the Samurai bridge, right after The Five Kage Summit and Sasuke's fight with Danzo. This a straight up fight with no supports; so not a lot goes into the strategy in this fight. Fight with preserving health in mind while getting a lot of attacks in. Once Sasuke's health bar is a little above the half way point there will be a short cutscene and an ultimate decision. Honestly neither of them is more difficult than the other. You will just have different flashbacks based on your choice.
In general stay back if you only have 1 substitution jutsu so you don't get caught in one of Sasuke's jutsus. Use the rasengan + a lot. I would also have at least 1 healing item on you just in case. The fight isn't hard by any means its just better to be safe then sorry. Once his 2nd health bar is down to about a quarter a series of quick time events will begin. If you have high health by the end of the quick time events you should have your S rank.