If your hexes are small enough, they can still give smooth natural-like results.
Only on a large scale, at which every shape gives smooth results, even squares (heck, the pixels on your screen are squares).
But I need a map that looks natural even if zoomed in a lot. Voronoi cells do that. At very large zoom levels I may have to add some noise to the lines seperating the cells, but that's easily done.
