Withered stomach on my vampires meant that they only earned silver at their wedding as taking the first slice of cake was a no.
I think the easiest weaknesses are withered stomach, sleep of the undead, fitful sleep (both ranks), and undead aura.
Fitful sleep doesn't seem to affect dark meditation, and really, if every once in awhile they have to spend an entire day sleeping, it's really no big thing. Undead aura does make for a little challenge but if you have the friendly perk you still get a big boost, and if you're in a popular club, it's completely irrelevant as people will start start out just a couple of interactions away from good friend.
Edit: The best thing to do is play around with them, though. It is only 1k to refund your points if you really can't stand one or more of them. I think they make the game more interesting. I love day phobia combined with the child of the moon (all three ranks). Weak during the day, strong at night. But day phobia is definitely not an easy weakness.