CNET editors did not review the Samsung UNC6300 series, but we did review a similar series of Samsung LED-based LCD TVs, the UNC6500 series.
According to Samsung's Web site, the main difference between the two series is the presence of Samsung Apps in the UNC6500 models. The two series also have slightly different styling, one colored "stone black" and the other "graphite." According to one portion of Samsung's Web site, the UNC6500 is also 0.1 inch thinner than the UNC6300; however, according to another section of the site, they're the same thickness (1.2 inches).
According to Samsung, the UNC6500 has a better contrast ratio spec than the UNC6300, which might contribute to slightly better black level performance. However, we don't know for certain as we haven't tested them side-by-side, but we suspect that any visible difference would be minor, at best.
For more information, check out the full review of the Samsung UNC6500 series.