Itachi. He's got that father/elder brother feel. He's great for that. U_U He'd likely give Sarada decent advice on life, take her out for dango, and crack jokes (since he does have a sense of humour-
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He teases people and is a troll. lol). He'd also be great at teaching her the basics in terms of jutsu, plus he's patient. But, he's not a pushover and can be strict when need be, so Sarada would still go far.
Neji... is a great shinobi, but doesn't seem like the type who'd be good around kids. He's too serious and would likely be too aggressive if they mess up (which children do all the time).
Gaara just seems detached as an uncle. He didn't say anything other than "Welcome home" and the conversation with Shikadai ended lol. Not him.
~Ignore the trolls who are skewing scenarios and leaving out details, as well as making up their own fanfics regarding Itachi. They're just showing either a) They couldn't read past part one of the manga, b) Trolling randomly on forums is the highlight of their life right now, or c) They just lack reading comprehension/understanding in general. It's him. U_U