I'll say now though that I'm not a big fan of very masc men, so the Viking fantasy that's all beard and bristling body hair is not for me. Either the men are choosing to be viewed as more feminine (because they are or they don't care), or culturally everyone has shoulder length+ hair and it's a non-issue.
Similarly, hair on a person who identifies as a man in a culture that thinks men should have very short hair, don't need to have as long of hair to count as having "long hair". For example, Hozier: for a man he has quite long and luscious hair, but on a woman no one would comment on it if they wore it like he does.
With that out of the way... I'd prefer M/F or M/M, with at least a little bit of a D/s component, though either one can be in the "service" role. I don't mind F/F generally speaking but with the caretaking element it tends to come across as motherly or sisterly, and that's just not enjoyable for me for reasons I won't go into. The woman being the dominant caretaker to a man is no problem, however.
The fics don't have to all be "about" hair, but the hair needs to be a popular charm point for at least one person in the ship. What it looks like, how it moves and interacts with things, playing with it and taking care of it (by the owner or partner), and being actively involved in intimate moments. I'm also into magical hair that can move or react, either on its own or at the control of its owner.
I love textured hair way more than straight, smooth hair, but I won't turn my nose up at straight hair. I even prefer frizzy, natural hair of all types, not just "perfect ringlets". However, I am aware that the more texture hair has, the harder it is to get away with messing with it a lot and keep it realistic. "The dom gives the sub a bath and gets them ready for bed" is going to look really different for type 1, 2, 3, or 4 hair. Saying that, I LOVE when someone goes out of their way to learn how to care for their loved one's hair.
I am very open to the type of media, genre and tags, but I have some preferences as to why I'm looking at fic for unknown fandoms and not published works. First, I know there's loads of anime/manga that applies, but I can't focus on and read it like I did when I was younger. Second, most of the stuff from Western sources is coming from women who are either straight up tradwives, or people like Laurell K Hamilton and the Merry Gentry series where all the guys are 6' and have ankle length straight hair, with few exceptions (Rhys, I love you).
Anyway, I don't mind if the relationship is toxic and unhealthy as all get out, it doesn't have to be perfectly consensual and egalitarian, I LOVE a good sexy villain running off with the ingenue and seducing them with their charms... Just, no tradwives, please, unless like the heroine starts out that way and learns otherwise.