i vote for varghulf,
he is a vampire, so can march, and take other units with him..
for a 1k army (that whats this topic is about), i can have a varghulf and a unit of direwolfs, rushing at 16 - 18" in 1 turn, so with just over 215 pts spend, i got 1 flank totally covered plus able to flank charge, or take out war machines and rearcharge..
though wraiths certainly are good, they lack the speed (though if you take black knights, it doesnt matter).
therefor, i guess it really depends on your other units.. i must say though that the extra rules for varghulf. vampire, regen, terror do tip the balance in his favour.. so my vote goes to var