It’s not just Obama v. Clinton today. Among pollsters, it’s Zogby v. Insider Advantage and Survey USA.
Insider Advantage shows Obama up only 4% in NC and down 4% in Indiana.
Survey USA has Obama up 5% in NC and down a staggering 14% in Indiana.
My guess is that Zogby will be farther from the final results than Insider Advantage (and perhaps than Survey USA as well). But then, I haven't done any polling in either state.
In the November 2004 general election, Survey USA got the state-by-state presidential results closest of 11 polling organizations studied.
UPDATE: As noted in the comments, Daily Kos has a nice review of 6 pollsters this primary season. Survey USA (4.7% av. error) has a wide lead over 2d place Rasmussen (8% av. error). In fifth and sixth (last) place are Zogby (9.8%) and Insider Advantage (10.1%).
2d UPDATE: In NC, with a large African-American turnout and heavy pre-election voting, most of the online commentators are predicting a huge win for Obama. So Zogby might be right after all . . . .
3d UPDATE, Tuesday evening: Right now Indiana is too close to call and NC is going overwhelmingly for Obama. At least in the closeness of estimates, it appears that Zogby is going to be a big winner as well tonight.