Are there any blatantly evil followers that I can sacrifice for Boethiah's calling?

You get an evil follower, Eola, by completing Namira's daedric quest. This requires you to do something quite evil yourself, though. You can also get a few evil followers from the Dark Brotherhood questline, but they are not eligible to be sacrificed.

I went with Marcuio (Riften) because he was really pompous. And it was him or the Whiterun guy with the ram-horned helmet that made a lewd comment to my char (female, because I'm a female). Being someone who gets tired of that in games, ....yeah.

The odd thing is that I take Faendal usually because the story line really seems to get you to walk a morally gray line at least, which I have no problem with, but he keeps my char in check.

SPOILER: If you go to solsthiem and do the 'unearthed' quest

once it's done if you let Ralis live, use him as your follower. It's soooooo beautiful.