Ok, just for the record I am a Sasuke fanboy, but I will try to be as objective as I can here.
I feel Sasuke has been a much MUCH more interesting character than Naruto throughout the whole series, but especially in Shippuden. Pretime skip, Naruto was a good main character. He was outcasted by the town, he had no friends and family, and had to bear a terrible burden of loneliness. He worked hard and got stronger, and made friends and changed some people's lives, it seems that all of Naruto's character development was done pre-time skip. I think in Shippuden, Naruto has been an unrealistic whiney loser. All he wants to do is bring Sasuke back to Konoha. Has Naruto ever even thought what would happen if he beat Sasuke and brought him back? Sasuke would leave the second he was healthy enough. What is Naruto going to do, permanently break his legs to keep him from leaving? When Tsunade informs them that Sasuke killed Orochimaru, Naruto goes, "does that mean Sasuke is coming back?" DERRR NO IT DOESNT YOU IDIOT!!!!!!! Does he even know Sasuke? He willingly left to train under Oro, not kill him!!! His goal is to kill Itachi you freaking moron!! And the fact that he has no variety doesn't help at all, Rasengan was cool about 150 episodes ago, learn some new moves will ya!
Sasuke is more interesting because he is always changing to new information, he isn't set in stone like Naruto. His backstory is just as interesting to me, if not moreso than Naruto's. Having his family and everyone he ever loved killed off by his own brother is a horrifying ideal, and having those bonds and losing them is more painful IMO than never having them like Naruto. Fast forward a little bit, and he was so set on revenge on Itachi, yet when Kakashi talked to him after his fight with Naruto, you could see Sasuke struggle with his emotions. He did have good friends, he had new bonds with people, yet his desire for revenge was so strong, had the sound ninja not showed up then it seems evident to me that he would have struggled more with his decision, I do think he would have chosen to go for revenge though. After finally getting his revenge on Itatchi, Madara reveals the truth (maybe) that Itachi was protecting Sasuke all along. Sasuke clearly struggles to accept this, as this would mean his desire for revenge has been pointed at the wrong people. After accepting Madara's words, instead of carrying out Itachi's wishes, Sasuke decides to use this new information and try to bring justice to the people who deserve it, Konoha's elders.
All in all, I think Sasuke will continue to be much more involved in the plot and he will keep developing as a chatracter, while Naruto is just kind of hanging around and along for the ride in Shippuden.
Edited 3 total times.