I went XTR because a) I like the noise level (or lack thereof), and b) I know how to work on a Shimano hub and have all of the tools. The fact that I got a killer deal on the XTRs helped too....otherwise, the White Industries were at the top of the list because they used a Ti freehub body and I like their service procedures. I believe that some of the high-end hubs (King, maybe?) require proprietary tools.

I build with DT Competitions (14/15 double-butted). Not too expensive, easy to work with, and available everywhere. You could do Super Comps or Revolutions (or comparable) to save some weight if you wanted. But that's a conversation for a real wheelbuilder, not some home shop hack like me.

I prefer to use brass nipples rather than alloy, despite the very slight weight penalty. There is nothing that makes me crazier than having to true a wheel with alloy nipples that have seized and having them round off. Brass nipples are more durable, are less likely to seize or crack, and only weigh ~20 grams per wheel more.

Have fun spec'ing your new wheelset!