Does “Aria the Scarlet Ammo” manga continue off from the anime, or does it turn into the spinoff? I'm considering reading Hidan no Aria after watching the anime (a long time ago). I remember when the spinoff came instead of season two and was fairly disappointed.

Does the manga continue with the same main characters?
Actually, there are more than 1 manga series: 


Hidan no Aria: started as a light novel, got adapted into manga &amp; anime.
Hidan no Aria AA: started as spin-off manga, got adapted into anime &amp; light novel.
Hidan no Aria-chan: a 4-koma spin-off manga.


So, to answer the question: yes, Hidan no Aria manga continues from the anime, which is an adaptation to the original light novel. The anime ends at volume 3 of the light novel, which is around volume 8-9 of the manga.



Note: Hidan no Aria manga continues as Hidan no Aria - Shiden no Majo after volume 16.