I haven't said anything about Blade Ward yet because I haven't had time to check whether the
old model and code from 3.3.x is still valid.
Presumably it is, which means it probably still comes in around 20 DPS, slightly below the other enchants. I'd love to revisit the code, but I have enough other things to work on that I don't see myself having time to update it before Cataclysm's release, at which point Blade Ward will probably end up being irrelevant.
My advice is that if you're interested in a balanced survivability/threat enchant, Blade Ward and Blood Draining are both reasonable choices. If Mongoose still works as advertised then it's probably a viable choice too (I had heard rumors it was nerfed in 4.0.1, but I honestly haven't had time to look up the details, so I can't really make a definitive statement on Mongoose). If you're looking for pure threat, I would slap accuracy on a slow weapon (and reforge some hit elsewhere into something else if it puts you over hit cap).