This topic might’ve been brought up a long time ago, but I am curious about everyone’s opinions.

I use both a soft camping cord and a hard camping cord, the width of the two is about the same, at around 0.4cm. I don’t brace them, I use a variant of the sheepshank knot to make the pouch.

I prefer both in the same sling like the one I’ve recently made

I experimented a lot and I prefer sisal type fibre cords with a diameter of around 4 mm, modular sling so I can easily replace cords. I usually do a 4 strand round braid or if I am in a hurry, a 3 strand braid made from loose fibres. These cords are very light and don't require a lot of fibre to make and I can carry plenty of spares. A day of constant hard slinging is usually enough to make the release cord worn out, with all the abrasive stones I use. I really like a smooth release cord end over any type of retention knot/toggle and I feel sisal allows me to do this best. I think this feature in slings probably improved my accuracy the most.