Leather cord is my favorite for stringing trade beads - it comes in various thicknesses and has a superior feel when worn against bare skin - a consideration when leaving the back 7-8 inches of a necklace with no beads. I have found that the various nylon cords like C-Lon to be very uncomfortable when used like this.

Leather is not a permanent stringing material however and must be replaced when it gets worn. It also can break at thin spots or worn spots.

A note on bracelets - beads on bracelets get banged up a lot, especially if they are large, or the wearer is clumsy like I am! For this reason I make very few bracelets with collectible beads.