Glass cabinet for me as well, some under its own acrylic cover.
I regularly pick them from the cabinet to get a better view.
Storing them in the open will eventually kill the finish. The bigger dust you can brush off, but the very small particles create a slightly sticky layer that you can only wash off. This by itself will be bad for the paint finish and groundwork.
Things will still get dirty over time even behind glass, but at least it is a slower process.
And behind glass there's a smaller chance of you, family or pets knocking them over accidentally.
There is one treason that may make me reconsider the glass cabinet however. I live in a hot and damp climate and I noticed that mold starts to develop on some of my figures. I am still experimenting with how to prevent it from forming, but suspect that the lack of air circulation in a glass cabinet or dome doesn't help. I've tried to add dehumidifying bags to the domes, but mold still develops. I am now trying to keep the cabinet doors open at night, to get air circulation for some of the time. We'll see...
Cheers,
Adrian