Considering that except for capsule rounds (where you can apparently get away with using 1/5 of a dose), the cost of the toxin is going to be the same; it's just a matter of your range and the cost of the firearm round / injection bolt / injection arrow / injector needle. Me, I'm a capsule round person - unless, as it now turns out, you have to hit them from further than 50m out. Then I think I'd go with the standard daikyu and injection arrow.