Mainline straight through to the lead.
I did all the experiments on leadcore years ago and the simple answer is, I don't use a leader at all unless fishing at maximum distance, and it's always with run rings and running leads.
The leadcore especially wasn't safe, beads stick, rigs don't eject, and helisafe doesn't work as the leader needs the lead to stay on to eject the rig.
In fact I don't even like helicopter setups as bite indication is so bad compared to inline or pendant setups.