What make/model of tandem and what's the rear spacing? 130mm, 135mm, 140mm, 145mm or 160mm? It is important to know as not all of these hubs come in all the necessary widths and configurations for thread-on drum brakes.
However, pending the additional info....
CHRIS KING TANDEM:
Of the three you list, Chris King's tandem hubs are the "new best" with regard to durability. They are also quite light even with the steel cassette body which IS recommended for tandems; however, they are also the most expensive of the tandem hubs on the market. We and many other teams have these on our off-road tandems primarily because they are the only hubs we have not been able to routinely destroy when subjecting them to the rigor of two-up, technical off-road riding.
Excellent seals and a bomb-proof engagement system. The only downsides are -- they aren't completely user-serviceable (unless you buy the Chris King tools needed for the job), 36h drilling, and you can't use them with a drum brake. Ouch!
WHITE INDUSTRIES RACER-X:
My next pick from your list would be White Industries' Racer-X hubset. We have these on one of our road tandems -- but without the left side threading for the drum brake -- and they have thus far been a great hub. They are very light -- lighter than Chris King -- but use a less robust pawl engagement design than Chris King. However, I've not heard of any pawl related problems with these hubs. The only bit of negative feedback that I am aware of had to do with the bearings on the previous model of hub sold for use on tandems: the Speed Racer hub. However, on the bright side the replacement bearings have all been holding up fine. You'd have to check with White to see what drillings they are offering for tandems. I'm pretty sure they offer 36h, 40h and 48h. A good friend in Austin, TX, put together some photos and a narrative description of the White Ind. hub overhaul process that you can check out on our Web site if you want to see the "guts" of their hubs: http://home.att.net/~mark.livingood/.../whitehub.html
As for the DT/Hugi hubs, I'll defer to Brad who is actually using them.
PHIL WOOD FSC:
Not included on your list are the also mentioned Phil Wood hubs which remain my personal favorites for the "overall best" tandem hub -- we have two sets for our road tandems. They are a bit heavier than the others but it's not rotating weight so the penality is minimal and far outweighed by other considerations. I have a Web page that provides an overview of these hubs (I like them that much) which you are more than welcome to peruse:
The one thing that I don't mention is that Phil Wood hubs have a reputation for being an integral part of well-built tandem wheels just seem to last and last with nary a broken spoke. The folks at Phil Wood attribute it to the way they form their spoke holes -- stamping vs drilling. My favorite "feature" is that they are completely user serviceable without the need for any special tools. They have model specs to cover every rear drop-out spacing that tandems use along with all the various drilling options.
Frankly, I don't think you can go wrong with any of these hubs -- well, at least the ones that can be adapted for use on your tandem and drag brake.