(Disclaimer: I'm a PhD student in real-time operating systems at UNC.)

Each program has its own strengths, and simply comparing between similarly titled classes is an unfortunately poor metric. (Eg. At UNC, OS is really an introduction to C and OS concepts class. The Operating System Implementations class sounds more similar to CMU's OS Class.) Academic programs need to be compared holistically, and only if one is consistently worse than the other do you have an answer. (Otherwise I could go and claim that UNC is better than CMU because our real-time group is much better.)

Of course, that's too much analysis for most people (including me), so I would argue that looking at where graduates work is typically an okay proxy for undergraduate educational quality.