I give no shits about Naruto and Sasuke, so anyone else really. If I could pick, I'd say either Gaara or Rock Lee, for no other reason than that they're my favorites.
If I'm going to be serious, the series wouldn't have much of a direction if it were centered around Lee, even with character development, though I'll stick by my convictions and say that a sand siblings spin-off would have been nice, and in extension, at least during part 1, Gaara had enough material to be the main character. He was Naruto's foil, so it's very easy to expand on that.
Itachi could have worked and even, dare I say it, Sasuke. In vested interest, Sakura also. It would mean the plot would have to include her.