Tales of Vesperia was blank white inside, I wanna say I have other games that are just blank but I can't recall any other specific examples. I do love that the clear case lends itself to more publishers putting neat art inside, though.Switch, easily.
The cases not only have the perfect size, but they all include a reverse artwork. Sometimes it is full art, sometimes instructions, but the cases/artwork always have something inside.
My vote is for PS1 jewel cases, though. Despite not necessarily being my favorite visually, I just loved that the cover art was the front of the manual and the feeling of sliding it out was something I loved back then. Bonus points for multi-disc games with a DIFFERENT art on the manual than what was on the cover.
Man, I miss instruction manuals.