Where do you typically fly? In NC i'm guessing you would mostly have to connect in CLT on US or ATL on Delta.

CLT flies many places, but not as many places as ATL.

I've never tried to redeem on US, but on Delta it is ok. You will rarely find the 25k domestic "Sky Saver" tickets. The website will search NW also and I have booked online rewards that way, but don't expect 25k domestic tickets on Delta...

ETA:
Also Delta only does Elite status by miles, but US will do miles or segments. Considering you will most likely have to connect that is in US's favor, but US just got rid of the 500 mile minimum so that cuts into miles earnings.

I like the Delta staff better, but on regional jets you deal with other carriers and they have varying staff attitudes.

Delta doesn't shove credit cards down your throat like US does.

Both airlines have "unlimited" upgrades for elite customers based on status...but you need a plane with a first class cabin to really matter.