I always used a .021" (50lb) butt section when tying leader. In the leader
tables I have, that's an Orvis Standard trout leader. I bought an Orvis kit, and
just replace the spool as I run out. As you can see from Frank Whiton's
leader formulas, you'll run out of butt and tippet more often than the sizes
I used all blood knots for the first few years, and then switched to double
surgeon's knots for sections .011" and smaller. Lately, I've been using knotless
leaders, but not everything is peachy: if I get a wind knot, I cut it out, and
tie the leader back together; tippet grows short, so more tippet gets knotted
on, etc. So, do we ever have a truly knotless leader? I dunno....
Tip on Blood Knots: You can't really hold four ends with two hands, without going nuts. I use two pairs of small hemostats, and clip them on the tag ends
after they go through the yet to be cinched blood knot. Once both tag ends
are clamped, I just let the hemostats dangle, wet the knot (spit), and then
pull the leader sections. Jiggling the leader sections while cinching will cause
the hemostats to give that added tensions the tag ends sometimes need.
You can buy a tool for blood knots, but I've never used one (too cheap).