With all the mess that has happened in the Aki-P empire lately I've been thinking that Nogi might be the best-run idol girl group in Japan. If not them, then who?
AKB is clearly out of contention, as they've had more scandals than you can count. HKT (Sasshi), NMB (Milky) and SKE (maybe) are also out, they've all had a long time to become messy.
But things get more interesting when we compare Nogi (almost 6 years old) to some of their junior groups.
NGT48 only debuted last year but with members like Rika and Katomina they're just inherently messy even without scandals.
As for Keyakizaka they've been a soap opera since before their debut in 2016. A member got kicked for dating her teacher, nazi uniform scandals, member hiatuses, fainting, rumours about them leaving the group or joining Mexican dramas, there's been constant drama for 2 years now!
Nogi on the other hand has been surprisingly free of any mess, which fits in nicely with their pure concepts and image. The only real scandal they had was when Sayuringo had an affair with a married man with kids.
Outside of the 48 and 46 groups Morning Musume has also had a lot of scandals.
As for the rest there are a lot of groups who haven't any scandals on the level of Sayuringo, but they all tend to have much fewer members so you can't compare them directly.