I like to have the smoothest connections between my fly lines and leaders. So, no loop to loop connections for me. So, I mostly use some type of nail knot connections. And, if need be, I can and have tied a nail knot on the stream by wrapping the leader around my index finger.
At home, I sometimes use a nail knot Tie Fast or similar knot tying tool, or here are a couple other ways I’ve attached my lines and leaders:
Insert a bodkin about 1/4” or so into the end of the fly line, and push it out through the side. Insert the leader into the hole you’ve created, and tie a nail knot above where the leader protrudes through the side of the fly line.
View attachment 1641239582