I would have to say and only half cynically "any knot I can actually tie, that stays tied" because there is no getting round the fact that I have cognitive disabilities in that respect. I could not tie a pair of shoelaces until I was 18 years old and they still have a nasty habit of coming undone.
Any knot I want to rely on, I have to tie at least one security knot on top of that to be sure it will hold, if it works it does, if it doesn't oh well have another go. I have to keep going back to the books all the time, just doesn't stick in my brain.
Lets take the time I needed a tow to get my car out of a ditch, no use tying a knot, much better with strong webbing and friction buckles