Tempered Glass, not tinted. Not a lot of people enjoy the Tempered Glass trend, but I want to show off my components, not hide them. And plastic just doesn't have the same transparency as glass does.
Given a decent layout, such as the case in this giveaway, the next most important feature is modularity, the ability to purchase add ins and additional custom pieces for a particular build. For example, white rimmed tinted glass instead of the customary black, or a new front control panel when USB 3.2 becomes standard.
I've got to go for balance- choose components that balance and support each other- none that are either underpowered or overpowered or you have wasted money on the whole build.
Most important feature of a case design for me is a targeted design, a case that does what it sets out to do, does it well, and doesn't do anything else (not discrediting style/design here, that's a target too). Particularly important is no wasted features. A great example is so many 'gaming' cases that still have racks for a dozen hard drives. No one's home build is going to use more than one or two.