I have a hard time putting other peoples OCs in my favorites, I'm picky. But I send to go for cool/calm types that are a bit of villainous. Like Shintaro xP I tend to make my OCs like that allot too. OTL
I don't think I have a particular preference but I like the ones that stand out to me. Characters that fit into a trope and then simultaneously subvert it in some way, characters that have a profession or a trait that I've never seen before. And sometimes I'm drawn to visibly disabled or openly homosexual characters because those are kind of uncommonly seen in Naruto OCs (even though I have a sizeable handful of gay ones myself). I also see a lot of experiences (ie dead parents, dead siblings, basically anything traumatic) that aren't handled with the greatest amount of realism so I appreciate when they're handled realistically (it's a rather personal thing for me given that both of my parents have passed away)
I don't think I have a favorite type. My favorite Naruto character is Ino, but the first OC I created was completely different from her in personality. And I always like to try and create different OCs. :3 But what about you?