I think it may be Hoyt. If AB kills Eric then there would be a very VERY angry audience (and I think it would be too much for many of the readers who love the books and tolerate the liberties that AB has taken).
AND HBO could lose some viewers (and subscriptions (Im actually one of those who only pays/subscribes for HBO when True Blood is on)).
Jessica seems to have developed a serious fanbase (a la Lafayette) so I think AB sees great potential in really developing this character...particularly if we have the opportunity to explore her dark side in the unfortunate event of Hoyt's murder/death.
It seems pretty obvious that the King has to die ( ) because his character has become so extreme that they can't keep him around and explore other storylines with sookie, bill and eric (it would not make sense--all the king would try to do is kill them and they cant pretend like he went on vacation or something).