The US Title is more prestigious than any NXT title, just because it's usually shown on Raw, Smackdown, etc.
I'm not sure, however, what they're doing with the US Championship anymore. The other day, I was chatting with a friend about the "State of the WWE" and neither of us could recall off the tops of our little heads who the US Champion was (pretty amazing, considering the fact that I'm a tremendous fan of the Shield, although I like Rollins more than Ambrose...just a matter of taste really). But, between us, we can almost always be counted on to be able to reel off the titleholders in WWE.
My point is that I think they've lost what to do with the US Title. The WWE Championship is for the main event guys, the WHC has become an upper midcard belt, while the IC is the true midcard belt (of course, the tag belts and Divas belt are obvious). This leaves the US Championship without a place (there's not really a reason to have a lower card title or even a lower-midcard title). Maybe showcasing it on NXT means that it's going to be "sent down to the minors", so to speak. Maybe it will be a second "main event" title for NXT eventually.
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