What a great thread, QuelleFromage! My own limited experience with Box, observing my own bags and friends' bags, has made me curious about this topic as well.
I'll add what little I can to the subject from my own collection, but will be interested to see other accounts too.
Shown here, four box bags: going clockwise from top left, a 1981 Kelly, a 1969 Piano, an undated Cecile that I suspect is from the 1970s, and a 1986 Trim.
The 1969 Piano is the plushest thing imaginable. You could use it as a pillow. It's not as shiny as my other bags-- it glows from within. I'd compare it to a South Sea pearl versus a freshwater pearl. It's also very very smooth, as you can see in the detail shot. This one is my favorite to touch.
The c.1970s Cecile and the 1981 Kelly are very similar. Both are stiff and shiny, and easily get fingerprints. The leather is thinner than the 1969 Piano's. Both bags show a lot of surface texture, but it's very regular throughout.
The 1986 Trim has a deep glossy shine that the photo doesn't really capture. It's almost mirror-like. The leather feels very buttery to the touch: not as plush as the Piano, but delightfully silky. The Trim is definitely my favorite in terms of the leather's appearance. It also has the most surface "interest," with great irregularity of texture. It's the least susceptible to scratching.
Ah, box. I want more!