chiltepin Whichever the current iso ships with.
The current ISO, as far as I remember, ships with linux 4.something (4.2 ? Really don't remember)
The problem is, the current drivers are built against the latest current kernel in the repos, which is linux 5.x (not on Solus at the moment and I'm getting old, don't remember the exact version): if you try to install them on a linux 4 kernel, bad things happen.
Full update first, drivers later.