You might want to play around on Excel Sports' website to compare the weight and price of various builds. Certainly, from a weight standpoint, the DT Swiss hubs are the lightest choice (they're a bit lighter than CKs and a lot lighter than Ultegras). Ultegras are also a fraction of the cost of both.

There's a pretty intense debate as to whether loose bearings are easier to service than sealed cartridge bearings, and I won't even begin to weigh in on that one. That debate aside, I think just about everyone agrees, however, that Shimano hubs are very durable and easy to service. I just had an experience at my local bike shop--which is otherwise a good shop--that makes me doubt whether they really understand sealed cartridge bearings. They don't build wheels at the shop and are disadvantaged in that way. Whatever you get, I would suggest reading up on how to service and adjust them before embarking on your trip. And bring some extra spokes as was previously suggested.

Frankly, if it were me, I'd go with an Open Pro/Ultegra build; 28 2x front, 28 3x driveside, 2x nondriveside rear. But I say that because weight on a cross country trip would not be my biggest concern. If weight remains your bigger "want", then I'd go with the DT Swiss or (although you haven't mentioned them), White Industries.