Having lived for a very, (very) brief period of time in both places, I would personally probably pick Northwestern solely due to location as I love the Near North Side MUCH more than Nashville. But if your friend has no preference for location (or love both equally) and is unlikely to want to pursue a dual degree, I agree with the other comments that Vandy seems like the better choice by program alone due to P/F, research time. Neither class size seems like a concern to me.