I use the regular ole clinch most of the time on nymphs and dries trout fishing.
I go to a trilene or palomar on the bigger flies for trout or when there is a good chance of hooking a large trout, and always when carp fishing.
I’ll use a double Davey on the tiny stuff (smaller than 18).
Streamers it’s a non slip mono loop or trilene or palomar depending on the action I want outta the fly.
Leader to tippet ring trilene or palomar - tippet to tippet ring- trilene or clinch.
Albright for backing to fly line.
Fly line to leader perfection loop to perfection loop - or a nail knot with a little uv coat on my euro rig (needs to be smooth as your constantly going in and out of guides)
If I’m building a leader, blood knots.
If I’m setting up a dropper rig I’ve been using a triple surgeons mostly but experimenting with others. I like the triple surgeons for its ease to tie, but not for its tendency to not seat all that great unless you are really careful with it. I’ve tried the J knot, which I like the strength of but it’s a bit of a pain to tie cuz of the longer strand of tippet to feed through, but with some practice I think it could be a good alternative (it’s actually really kinda a triple Davy between two lines). I’ve also tried the seaguar which is good but I don’t like the way it tends to twist around itself when tying it. I just discovered the Japanese figure 8 which is basically a seaguar knot without the three twists in the loop... it’s just a half twist. I might switch from the triple surgeons that the figure 8 to test it a bit. I like the simpliciTy and apparently it’s strong. If it’s stronger than a triple surgeons, forget it I am switching.
I’d be curious to hear if anyone follows a similar approach. It seems like I use more knots than the average guy for different purposes / fly types, etc.