I think how they fit depends on what shape you are and if you've any problem areas.
If you're lean and long legged then maybe you don't need Diane, but if like me you suffer from ducks disease and have a couple of muffins lurking around that need to be catered for then they are brilliant. I have a few pairs of these and they are all incredibly comfy, and some fit differently, well they would as some are skinny and some aren't, and I take that into account when I order. So I have some in my standard HS size and a couple in a size smaller.
If you watch the on air presentations the presenters usually give you clues, other than JR of course lol.