I am not going to deny any of the teams mention here on this post, but when people thinks of team they think of the strongest and unbeatable, but forget about good teamwork. Meaning one must have a good knowledge of one's skills (ups and downs). The thread here mention is what's the best team, not the strongest, meaning who makes the best match in pairs or threes.
Nagato and Itachi are a good team, but they fall under the strongest team, not the best unless best would have meant strongest. Nagato skill is not in sync with Itachi's, so is Itachi's. Nagato ways of fighting would not benefit Itachi's, they are both individually strong, but none of them would be in the same page, even with their intelligence. they would win, but not for their teamwork, but because of their individual strength. If they're fight a stronger enemy than the both they would lose.
Best team would be Hidan and Kakuzu, both knows each other way of fighting, and are undead. Kakashi and Shikamaru, I'm surprised that no one mentioned that. Shikamaru is very smart, the smartest, and Kakashi is very skilled and also smart, master strategist. They would make the best team, they even gave both Hidan and Kakuzu a run for their money. They don't have those destructive or immortal, and indestructible power, but they can win.
The Ino-shika-cho, their kekkei genkai benefits each one of them, literally fighting them would be extremely hard even for the strongest shinobi.
Kakashi and Gai, they knew each other since they were kids, and know of each other's extent. They would make the best team due to knowledge, and Gai is very strong and fast, Kakashi is an assassin type ninja.
Yeah the Gin/Kin brothers they make a very good team, and they're both individually strong.
Team Orochimaru, Jiraiya, and Tsunade, due to years of knowledge. And they're one of the strongest in Naruto.
Kisame and Itachi, definitely.
That's all I can think for today if there's more let me know.
