Although there are such things as undergraduate masters courses, they're not equivalent to a postgraduate masters. From what people in admissions have said to me, a postgraduate masters course is more impressive than an undergraduate course mainly because the manner in which people are taught is quite different. In my experience, the postgraduate masters I'm doing is far more 'grown up' than both my undergraduate degree and the final year of several of my friend's MSci courses. In my friend's undergraduate MSci year they were very much treated as one of the crowd and their projects were pretty much a waste of time whereas in the projects we are working on in my MSc, we're working in the same research groups and alongside PhD students.