Should I join a Bujinkan, or Koga-ryu , or Iga-ryu, ninjitsu school\dojo\club? I KNOW it's not historically real\not useful in real fights..i see it as cool larping: samurai armor demons, camping and doing "survival ninja skills", ancient weapons, cool ,Shinto lore, etc
>the other students, Soke, will for sure believe in all this..I'll play along and, keep my mouth shut
Bujinkan is the most popular\ biggest one, but a bit lame unless you're a high-tier Soke? Koga and Iga ryu seem much more obscure and, thus, fascinating.

Definitely choose Bujinkan. Although historically ninjutsu is not a close combat martial art, Bujinkan includes ancient and authentic Japanese fighting skills. Bujinkan has a lot of exciting techniques and lore. Most likely, those Iga and Koga schools you’re referring to are complete nonsense made up by some crazy person.

By the way, soke does not mean teacher. Soke is the head of the ryuha and the guardian of its tradition. A ryuha has only one soke.