I would like to agree with the Wraithlord idea, but as he wants a competitive army, I won't support the idea of taking them.
Truth be told they are fairly good, but with the amount of heavy weapons present nowadays (and not those just on tanks) they tend to die very fast. Being so tall, conjoined with the dodgy cover rules means they can't hide for shit. BS4 isn't stable enough to provide a good weapons platform in my eyes and a TL-BL is just grossly priced.
2 Attacks, even with a wraithsword will achieve jack shit in assault, as no player with an IQ over 50 will let him get into contact with units that he would be ideal against (non-SS termies, San-Guard etc).
WWs are great, I love them personally, but they cannot perform ant-tank without pumping a lot of points into them, and even then...BS3. And with AV10, even boltguns can piss all over you.
IF your opponents are willing, the Forgeworld Hornet is a fabulous bit of kit. 3 of those can cause quite a bit of damage to enemy tanks, but sadly, do take up a lot of board space.
In general, the Eldar lack a cheap BS4 vehicle capable of anti-tank. Dark Eldar get the Raider..which in turn can then acquire a 5++ save. It's cheap, it carries troops and can destroy any tank. Although it's over looked in favour of the Venom, that's only because the DE get Ravagers and Blaster Trueborn.
I seriously cannot wait for the new book. Everything needs something fixing bar Eldrad. Here's a thought...DA with a weapons platform? Yes please.