I think they also look a little different. I mean, all those bags under eyes etc.Try looking for exceptionally old short-lived races (avoid elves), get them to your court and start carousing with them until you befriend them.
However, I'd stick with Molag Bal. Vampire infestations are rather unreliable, as you might not be attacked at all, you may be attacked yet kill the vampire assailant without as much as a scratch, etc.; and Molag Bal is pretty reliable. You can even become vampire in a few days if you have a big hoard of artifacts and don't mind chugging excess ones into domineering grasp of Molag Bal. Outside of Molag Bal being interactive (e.g. not aloof), there is no RNG involved.