Just to be clear, this loop design I cooked up is for combining different fly line segments mid-length in the head to create hybrid (float/sink) systems.
The most common approach for leader to line is a nail-knotted butt section with a perfection loop.
Some new lines (e.g. Rio outbound) come with a loop already in the line which is great.
Braided are also good but very visible and prone to loosening when the line is under pressure (fish) and the back end hits a guide.
Use either a perfection or surgeons loop on the mating end of the leader butt.