If you're new to tube rolling, like I am, and just want to hear a more than subtle difference in tubes, try comparing a Mullard CV4003 (box plates) with a, say, Telefunken 12AU7 (smooth plates). I find the Mullard to be too mid-centric, and the lack of top end frequency energy makes it sound unnatural. The Telefunken's mids have some of that holographic effect which I find very pleasing and overall is much more neutral. YMMV, of course.
-Raymond