welcome josh
The best results for me is 5mm nylon cord braided 3 strand with a split pouch (take a look at
3 strand braid sling step by step in this section of the forum) it's nearly unwearable and undestructible.... split pouch is a bit tricky to use at first but it works ok with a little of training.
Also i've made some slings with 5mm cord and woven plaster, it's very easy to make and it makes a decent full pouch, so its easier to sling with it. Woven plaster is my 2nd choice for a sling.
As soon as possible i'll post how i make this kind of sling step by step with pics.
Other materials i've used as pouches are leather, (it's hard for me to find the one who is though and yet flexible enough, and i find it expensive) 5cms climbing nylon strip and strong canvas but holes end ripping and stones tend to tangle on the cords i've used to tie the pouch.
Woven slings are cool too, but i don't have the patience to make one myself