I usually use a supreme sorceress, either a dagger, or a focus familiar dark pegasus rider. The second wizard is usually a tome of furion and dispel scroll wizard, either on foot or mounted on dark steed. The third character is almost always a master, with GW, seal of ghrond, and a decent mundane armor save. If I feel like splurging on characters, the 4 character is a death hag with the cauldron of blood. Sometimes I skip the master, and use the cauldron. Sometimes I make the master a BSB, sometimes I make the death hag a bsb. It really depends on the list.
All that being said. I almost always use dark magic. It has a great default spell that helps against opposing shooting. It also has number 6, which is a huge block busting spell that gets around magic resistance. (it doesn't target) The other spells all have great applications, with only doombolt being redundant.
If I am facing a knight army, or any army that has universally good armor saves (like dwarves) I take lore of metal. It has solid spells overall, and when the big one hits, it is almost sure to be worth the effort. (entire knight units gone in a blink type good)
Lore of fire has its place, I used it quite a bit when I see plague bearers. I also had good luck with it against VC, as wall of fire is really effective against them.
I don't really like lore of shadow much, as the default spell is pretty meh for dark elves. the other spells are pretty decent, so I might have to start to try it. It just feels that Dark lore is better.
Lore of death is particularly good against armies I haven't faced much of, so I will reserve comment on it, since I haven't had to use it yet with DE. I have had good luck with it with other armies.