Brad or Finish Nail Gun
for all you fully armed and operational weapons out there, remember there are wires and pipes inside walls.  usually the min. setback is 1 1/4 from the stud face.  so if you put a 3" "finish" nail through a 1" casing and 1/2" drywall, you are well within the realm of punching a hole through something wet or something sparky.

we have been using nothing but 18ga brads for 20 years to do everything from trimwork to cabinetry.  never had a warranty callback for any of it.  

remember its not the size of the nail, but how you use it.