Well, imo Madara has a better personality and beats Sasuke in the "badass character area" no doubt.
But in terms of character development and character story, I'll give it to Sasuke.
His character development:
-He had gone from an innocent and loving child to a heartbroken, sad kid as a result of a bloody tragedy.
-Then as his loneliness and reflection about Itachi's manipulative words progressed, his grief transformed into hatred.
-Upon being introduced into team 7, Sasuke was cold and detached, but then grew to care more about his teammates.
-As more time passed in Team 7, Sasuke saw the brightness and happiness in teamwork and shinobi life. Hence he abandoned his goal of revenge.
-Itachi's visit to Sasuke made him relive his clan's tragedy. Naruto beginning to beat him made him think that he is not powerful enough. Then came Orochimaru's tasty offer. He knew he cannot live a normal shinobi life, thus returning to his avenger life.
-Sasuke built upon his hatred even more in hopes of beating Itachi.
-After killing Itachi, Sasuke was neither excited nor sorrowful, showing his doubt of his freshly achieved goal.
-After Sasuke learned that Itachi was only trying to protect Konoha and Sasuke himself, and that he had killed his brother because of a lie, he broke down in regret.
-After grieving, Sasuke did not care about anything but inflicting Konoha the same pain that he, his clan, and Itachi suffered. All the pain and grief pushed him to the brink of almost insanity.
-After the speech Itachi gave Sasuke before he left, Sasuke began to question the way of shinobi and the way of his current goal. He visited the previous hokage and learned more about the shinobi system.
-Sasuke came to conclude that revenge was pointless, and decided that he will change the shinobi system so that no one can experience what he had experienced.
-Sasuke decided to break all his bonds with Naruto, especially, and with Team 7. He also broke himself away from the past.
All these, chronologically listed, are points of Sasuke's development throughout the story, which quite a lot. He is a perfect example of a victim of political flaws that plunged into dark paths and twisted goals as a result. That makes him a walking figure of "wtf" and "douchebag". No wonder he receives so many haters.
