I was reading through today and just saw someone write Xander was an asshole the first 3 seasons. You can look at one character and how you see them is completely different then how anyone else would. But I will play your game. Let's play a world with out Xander with in the first 3 years.
-Buffy is dead in Prophecy girl (So essentially no season 2) Angel couldn't do anything to save Buffy. The dead can't affect the living. (This also goes to speak to his character. Angel told him that the Master would kill him as soon as look at him. But somehow Xander wouldn't risk anything that doesn't involve his favorite person? Himself?
-Go Fish Buffy was about to be eaten/molested by the fish men swim team and Spike pulled Buffy out of the water. Wait it wasn't Spike it was Xander.
-Killed by death In the opening scene Angelus is just about to bite Buffy when Xander drives a knee to Angelus's face punching and kicking doing what it took to keep Buffy safe. Bonus Points for later in the episode it's Xander who stands face to face against Angel so that he can't enter Buffy's hospital room.
-Phases Funeral Home Buffy was about to get bit again by Theresa the student Angelus sired when it was Xander who staked her saving Buffy.
-The Zeppo The gang tried to force Xander out so they can save the world. He saved them stopping Jack Otool from blowing up the school. Had he not done that they couldn't have saved the world. He didn't tell anyone about it either which shows more character. He could have been bitter for being pushed away and said look this is what I did but he didn't.
Those are just the things I could think of off the top of my head. You don't like character and I get that. I don't' like Spike but you see him in a different light. I applaud that but you need to be able to look from both sides. I loathe Spike Angel Anya but I at least can acknowledge that they made contributions to the group.
There are two sides to every story and you should try to look at things from every angle. I get that there are people out there who don't like Xander. They call him boring or stale. I say this. Look at Buffy in the episode Helpless. She still fought the good fight because she was a champion. She had to do so with out any slayer enhanced strength or fighting skills any of that. It would be like Superman waking up and just be Joe Normal but still fighting. I respect Buffy for that. That being said this is who Xander was every day.
Xander fought the fight and he did so with out anything extra. He wasn't immortal. He wasn't trained or didn't have a calling. No magic or super strength. He did this because it was the right thing. He did all of that while risking his life.
More then that, in a show where every one in the Scooby Gang was doing all this super stuff Xander helped to keep them grounded in there humanity.
Does he have his flaws? Yes but show me a character in the show who doesn't. Xander's flaws or sins are a lot smaller and farther between then a lot of the other characters.