It's a psycho clown and a hot female vampire, who has been sleeping/sealed in a tomb for ages and have troubles with her daddy/family. The cause that she has been sleeping/locked for ages is that she is part of a prophecy that shall destroy the world.
Yep, huge difference..
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Hmm, tough to say. I wouldn't say she is my favorite, but I do like that Serana interacts with the environment rather than stare at me like a mooching puppy dog. Freyja is also interesting, though I don't like her voice (pretty cynical because I know some Skaal have accents and it's realistic, but it makes me want to pour liquid nitrogen down my earlobes). I don't really hate many followers either, unless I hate their voice or it's Cicero.
I always like hearing why people chose their followers.
Whenever I play a character in which I can reasonably fathom doing the quest for Namira's Ring (admittedly rare) I like taking Eola as my follower. Her fighting style is very similar to Serana (whom I also like to use as a follower) but I really enjoy the darkndss of her character, the quest to get her is kind of unique and I found somewhat shocking the first time I did it.