Will Serana treat you differently depending on the side you choose? I chose DG on my first and only Dawnguard playthrough and she seemed very amicable and totally backing Dragonborn's plots. If I go Vampire, will her attitudes towards me be different?

Nothing about her is different.

She treats you the same. She turns kinda evil on the Volkihar side though, I noticed. It feels weird.

I didn't. She has all the same lines, except for some of those when she first rejoins you.

I'm a polar opposite on that, my friend. She's the same little miss goodie-goodie no matter what you do. I don't see anything evil about her. It's kind of sad really.

I just picked her up and it's been a long haul to get her ass back home. I just want it to end. She's like a bad date, right now.

Good. I'm playing a Nord Dovahkiin who joins the Vampires without any intention to leave them alive, only to strengthen himself for the war against Alduin, and I don't want my character to come off as a power hungry scumbag when all he's doing is sacrificing his mortality for the greater good. Given Serana's importance in the storyline it's important that she knows my character wants only the good of Skyrim.

The one thing i noticed is if you decline harkons "gift", while hes casting the banish spell if you try to talk her she says we probably shouldn't be seen together right now or something like that