I'm pretty new at the world of shooting flintlocks, but I'll share my experience for what it's worth. When I got my first flinter - a .32 - the only powder I had at first was 2f Goex that I had purchased in anticipation of a .54 that I had on order. I used 2f for both charge and primer in that .32. It worked, but was inconsistent. I had a few patient gophers sit there while I flashed in the pan a couple times before killing them. Then I ordered some 3f and 4f Goex from Graf and Sons. I still like the 2f for the main charge in that .32, but the 4f is proving to produce much more reliable ignition.
My .32 has a considerably smaller touchhole than my .54, though, so that might be part of the problem. I haven't experimented with 2f or 3f for priming in the big gun after my experiences with the little .32. In that squirrel gun, the 4f produced more reliable ignition of both the priming charge and the main charge - fewer clicks and foofs, if you will.