[WraithLord]

Depends on the situation.

Pick one of the following: they are on the attack and laying siege to your castle, you are laying a trap or storming a castle defended by vamps. Point is if you can see them coming they are done for. Not saying its easy, but the fact that you have to be constantly fearing some judgment day weapon seriously limits your options.

Look at this that way: they will not usually be deployed outside of friendly dominion. That's already a serious disadvantage. Not much point in stealth if you can't use it to raid enemy provinces.
Granted, they are good on the defense but that won't win you games.

Personally, I'd go for the lords and use them for blood hunting mainly and defense when needed.