My take:
I think you miss the point. Emotions will do you in every time. The vampires are about backstabbing, gaining power, betrayal and sinister motives. There is no loyalty or honor to be found. When Serana first returns home, she drops you for a reason. Truth be told, I'm surprised they didn't have Serana try to kill the dragonborn after the final battle with Harkon. That's what a true vampire would do. That said, I love playing a villainous character....
As for the dawnguard side, I've done the quest line as a companion and I find it works out wonderfully. Being a nord at their finest.