Probably the Dawnguard. Isran is probably the most likable old curmudgeon to ever head a faction. Everyone in the dawnguard is some kind of coot, eccentric or madman. You have the priest that believes Arkay is talking to him directly. The jittery dwemer-tech scholar. The grizzly-wrestling wild-man that tames trolls with his bare hands.
Then you have Isran. Poor, paranoid, delusional Isran. Someone that's driven away everyone in his life with his doomsday-prepping and railing against the imagined vampire menace. Someone who was kicked out of the Vigil if Stendarr, a group of fanatical vampire-hunting zealots, for being too extreme. Who needs them, right Isran?
Only he just happened to be right this one time. A broken clock is right twice a day.
When you pit them against their vampire analogs in Castle Volkihar, there's really no comparison. I don't remember a single thing about the vampire NPCs in the Volkihar court, with the exception of Serana and Valerika. They're all sinister, foppish, conniving vampire stereotypes. With Harkon at the top of the pyramid as the most sinister, conniving and stereotypical.
I also have a soft spot for the College of Winterhold and The companions.
