Quick up unit review! Of course this is based on personal preference, but it gives the jist of how I see each unit.
First up, can't say much on the special characters as a) they bore me and b) haven't tried them in game. Quick summary – Kemmler seems alright, Mannfred potential use as hero monster rider, Konrad cheap for killy vampire. Everything else can bugger off.
Our primary lord choice, this guy can do it all. Wizard level 1-4, 100pts of Vampiric Powers and 100pts of magic items mean his cost skyrockets easily. However, at his most base level, although his stats are impressive he doesn't really contribute as much as, say, a Master Necromancer. Which is why you need to spend, spend, spend. Once you add a magic weapon, couple of magic levels, ward save, Red Fury and Quickblood he'll start approaching 400-500pts, but for that investment you get a model that is a Level 4 Wizard that can also kill 10+ models per round of combat. Resilient though he is, at this cost he'll be your general, don't stick him up against hordes with Killing Blow.
The second 'real' lord choice. The Master Necromancer comes at around half the cost of the Vampire Lord once tooled out. However he has typical human mage stats and so probably needs bunker to hide in. If you're only taking one, he'll have to take the Lore of the Vampires which, although a fantastic synergy buff lore, is not very destructive and so you'll need to spend the points saved from getting a Vampire Lord on some really hitty units like Varghulfs, Grave Guard or Blood Knights to get the killing done. Don't go for the bait and take loads of Zombies and Skeletons to maximise the benefit of Invocation, you need to kill enemies to win, not outlast them.
Strigoi Ghoul King
I'm really not impressed by this guy, in smaller points games you could probably stick Red Fury and a Dragonbane Gem on him and call it quits – but that's still a 315pt investment into a likely general that has T5, no save, and 5+ Regen. Far too squishy for my liking, and being a wizard with no mundane armour options, he can't improve that save much. Even the much loved Skabscrath, Curse, Gheist combo doesn't really strike me as a good choice – I'd rather have two, seperate, Terrorgheists instead.
Now, on like the Lord, Vampires can get expensive, quick. Unlike the Lord, you don't want this at all. Pick something to be good at – mobile Invocation to go with Knights, Forbidden Lore caddy, Fearbomb. Get bare minimum to do that. Done, dusted. Don't overspend.
Cheap enough to spam for access to Invocation, although Level 2 is worth the buy really. Real use for Necromancers is backup for when the general dies, and arcane items. The Book of Arkhan should be in every single Vampire Counts list. Cursed Book is also great so are the usual choices of Dispel Scroll, Power Stone and Forbidden Rod. If only the Black Periapt was cheap enough to take on Heroes...
The best choice of BSB, if you indeed want a BSB at all, and even then only really if you want a magic banner. Could also see him mounted in Black Knights to add a little punch, but otherwise unimpressive. Equivalent points of Grave Guard will outfight and outlast him.
Tomb Banshee and Cairn Wraiths
Well, the Banshee certainly has more uses as a hero than a champion for a Wraith unit, as you can stick her in something rubbish like Skeletons, protecting them with her Ethereal status and killing some stuff. Cairn Wraiths can do the same, adding kills to units while protecting them from non-magical attacks, although Cairn Wraiths are also perfectly capable of going off on their own to run down fast cavalry or small chaff units. Pretty decent for their cost.