All ideas begin analog.
On paper I can explore 4 or 5 (sometimes 10) solutions in a matter of minutes.
I prefer plain dot-grid paper, pencils, pens, and sometimes a Copic marker to add focus. Rapid iteration reveals a lot of ideas that won’t work, and a few gems that will. And it doesn’t cost much.
When the right solution begins to emerge, I switch to Sketch/XD/Axure/Framer or the UX app-of-the-moment to begin building a more polished project artifact.
Rapid iteration sketches from various projects.
As I go back and look at these sketchbooks, they seem sort of like comic books to me.
And why shouldn't they?
After all I am telling a story… from the user’s perspective.