The Farrimond Hitch is my favorite knot. Useful to tie a line to another line and have it adjustable, but strong under load and a single pull to undo it. Easy to remember, it's like a prusik knot.

https://www.animatedknots.com/farrimond-friction-hitch-knot

(overhand and double 8 are probably used more often by me, but not that versatile)