speaking about sisal, I do not believe that a complex braid is necessarily important, but rather the amount of material/ strands you have in the sling. especially in the retention cord. My sling is made of sisal 24 strands on the retention cord split to 12 for the belly, then reduced quickly down to 6 on the release end.(all done in fishtail braid) after 3+ months of heavy use it has broken several of the cords throughout the sling. This has not affected performance in the slightest. I have replaced the material on the release end, about 10-15inches, twice. the broken strands on the retention cord were just cut flush and left alone, and they have not pulled through.
As for wool, I will not use a sling made of it mainly due to the fact that wool looses much of its strength when wet. I wear a lot of wool clothing but do not find it even close to comparable to vegetable fibers, for performance in a sling. That being said I see it as a good option for stitching in a sling.
Jute vs sisal.
If you want to treat your sling with mineral oil,beeswax etc... I would recommend sisal or any leaf fiber, as these will naturally absorb the treatment more readily. Bast fibers have a tendency to resist treatment.(slightly Hydrophobic)
But...
bast fibers can have a higher tensile strength(depending on the species)
I think it comes down to personal preference within vegetable fibers.
What sling is the best?
Best for what?...Long distance throwing? Accurate mid range throwing? Most indestructible??????????
Best all around, In my opinion would be a sling made of natural fiber, braided, with a split pouch, of 2,3,4 branches for the pouch(personal preference again.) From what I have seen on the internet, and experienced myself, the best results have come from this sling type.