Riveting
I've got a QB, so I didn't need much help, and I don't have a lot of experience. However, I have spoken to a lot of people with decades of experience, and they seemed to agree that bucking is the more "skilled" task.
The key is to have a system of clear communication so that the shooter does not pull the trigger before the bucker is ready. This is the one they taught at Alexander Technical Center (if I recall it correctly):
1) shooter inserts rivet, places gun on rivet, and says "ready"
2) bucker places bucking bar on shop head, and says "set"
3) shooter rivets
4) bucker inspects and says "good" if it's ok. If not, he gives some indication of how many more "taps" are needed.
The things I like about this system are that the bucker is constantly giving the positive feedback to the shooter, is doing the inspections, and is generally setting the pace.
Obviously you want to make sure the shooter gets a bit of training before driving any rivets in very visible places.