I approach this situation from the opposite viewpoint....
I want a few knots (or hitches, bends etc.) to fulfil a number of tasks;
1, Attach a cord to a strong point
2, Attach to itself and slide to tighten/loosen a loop
3, Attach to a second line and move/grip as required
4, Tightly bind a compressible bundle
5, Secure two ends of cord together either the same or different diameters
... if these can be achieved with a "slip-finish" to allow easy un-doing, then so much the better
Add in a few knots of specific use and some decorative elements and I should be good to go!
What these knots are in actuality is open to interpretation at the point of use - I have been tying knots since I was a Cub Scout some forty odd years ago, certain knots remain as useful, others rise and fall in popularity as the mood takes me.
ATB
Ogri the trog
I sort of agree with everything said above.
The knots you use change depending on the material, what you need to do, and time.
I would go to
the dump and learn the basic ones in gilcraft book 7. Then you can tie knots you know how they work and it makes it easier to go on to the others. For example I would list the constrictor as one of my top five, all it is a clove hitch with a little change. If you can tie a bowline or a figure of eight you can tie all of the different versions. A bowline on a bight is useful as a make shift pully system. A lot of the climbing knots recommened are larks heads with more turns.
My top five
1. figure of eight - simple stopper knot but you can make loops with or even join ropes using two like the fishermans knot.
2. Bowline - as above really you tie the basic you can tie the others.
3. Sheepshank - same as above this becomes the truck knot or the cat shank it does slip in modern materials but there are ways round it. Worth learning because when you need to shorten a rope nothing is better.
4. Larks head - all of the others that follow on from this are useful for different reasons
5. Clove hitch - it start most of the lashings so useful especially if you want the rope back. However the constrictor works so much better but it is knot you do not tie in rope you want to use again.