It's the other way around. In general, polypropylene is softer than polyester. Polyester ropes can be a bit stiff. But it also depends on the type of rope and the thickness, not just the material.
Regarding knots, an
Arbor Knot is just a
Noose Knot with an added
stopper knot at the tail end. A stopper knot is necessary, because the Noose Knot on its own is not secure enough – it can slip and come undone. So a stopper knot is a
must, and the Noose Knot shouldn't be used on its own.
The Arbor Knot (which is a Noose Knot + stopper knot combination) can be used both for the neck and the anchor point. It works fine, and the upside is that you only need to learn one knot. However, for tying a rope to an anchor point, there are other options as well. For example:
Adding a stopper knot at the tail end is always a good idea. It's an extra insurance. Adding one makes the knot more secure and has no downsides.
For the neck, there are also other options, one of which is the
Poacher's Knot. It's a secure knot and still slides relatively easily. The Poacher's Knot is secure and can be used on its own (unlike the Noose Knot), but I'd still recommend adding a stopper knot. A stopper knot makes the Poacher's Knot more stable and prevents any slippage.
The
Hangman's Knot is not the best choice for the neck in my opinion. It would definitely work, but it doesn't slide very easily, and it's more difficult to tie.
