Most people have no need or use to learn a new knot after fishing for a while. Once you learn a knot, any knot honestly, and can tie it easily and reliably....they'll hold any fish you want and will only break if you hang bottom and NEED to break off.
So long as you know a knot to attach leader > fly line, leader > leader/tippet, and tippet > fly, you're pretty much set.
An 80% knot that you can ALWAYS tie well beats a 95% knot that you might mess up even once in a while.
I tried the Jack's knot and found it acceptable, but there's no reason to change from my knots that I already use and never have any problems with
. So it is interesting, but not something I'll use.
I tried the Davy several different times and with a variety of line diameters and just can't get the results a lot of people get -- mine slip as easily as an improved clinch knot where you cross 2 of the coils. Not for me.
I use the fish killer knot and the duncan loop knot and have never had one fail.