Definitely not distilled. Most of the best coffee cities around the world have tap water with dissolved solids around 150ppm. If you’re in a place like mine in Phoenix, the tap water is like 500+ppm, so we use RO and demineralize with something like Third Wave Water (or you can make your own for cheap). It’s super fussy, but the taste difference is real.
I'm a novice coffee enthusiast, and I was blown away by the difference appropriate water made to the coffee. I am now "making" my own water by adding optimal mineral mixture to distilled water. The results are superior to those with tap water ("raw" and filtered) or pretty much any bottled water brand that I've tested.