Are the Minami sisters canonically the purest girls in all of anime?
No, the boys yes.
There's nothing pure about them
Which Minami-ke seasons to avoid?
They're all produced by different companies.
Manga is better
Depending on who you listen to, 2 and 3, or either 2 or 3. I just stick with 1 and 4.
General consensus is that S2 is the worst but I personally found all of them enjoyable
Kana best girl
S1 >= S4 >>> S3 > S2
Hosaka is love, Hosaka is life