Dotted. Even better than graph paper if you draw a lot of diagrams/figures, in my opinion. I use Fabriano dotted saddle-stitch as a cheaper and lighter alterna

Dotted. Even better than graph paper if you draw a lot of diagrams/figures, in my opinion. I use Fabriano dotted saddle-stitch as a cheaper and lighter alternative to the Leuchtturm1917, for instance when I'm traveling or at a conference. The paper holds up to any non-calligraphic fountain pen I use.