A nail knot guy for decades, but last year I had a super glue period. Not always easy for me to get the needle in the center of the core, but it is a smooth connection. Had one leader break free - fortunately on a snag and not a good fish.
Now for the newest thing under the sun. Make a small loop at the end of the fly line - smaller than those meant for loop-loop connections (which I use for some dry fly lines so I can change leaders quickly on the stream). Then tie the leader to the loop with a clinch knot. Easy to do, small and holds well.