Stopper knots fall into two categories, single strand stopper knots and multi-strand stopper knots. Single strand stopper knots are tied without unravelling the rope first, this makes them easier to tie and untie, but also makes them more bulky.
Multi-strand stopper knots should be considered permanent, once in place your only way of getting rid of them is cutting off the end of the rope and tying a new knot. They are harder to tie, but can be significantly smaller.
Single strand stopper knots
Overhand knot
Double overhand knot
Figure of Eight knot
Barrel knot
The overhand knot is the most widely used stopper knot in shibari, and is smaller than any other single strand knot. It has the advantage that it is relatively easy to untie and retie if needed, but the disadvantage is that it can work itself loose and so needs retightening regularly. As all the other single strand knots increase the bulk that needs to be taken under wraps, using any of the others sacrifices utility for aesthetics.
Multi strand stopper knots
Open overhand knot
Thistle knot
Mathew Walker knot
Multi strand stopper knots are fiddly to tie unless they are something you tie a lot of, and they can not be untied. If you need to correct the rope’s lay because of high stranding you will need to cut off the knot, and retie. The Mathew Walker knot is somewhat longer than even the open overhand knot, or the thistle knot and so despite its popularity with some riggers the only benefit it brings is for those who are drawn to it aesthetically. The two key advantages they have over the other options discussed is that they are smaller, and more secure.
Video tutorials for tying multi-strand stopper knots: