I would choose whatever is sturdy. In the past I have bought threads that would easily tear and make it impossible to string beads. But it's your choice. Just one thing though:
Don't use the point-up pentagram.
"Fools do not know what they are doing. Energy is being sent up. It should go into the earth to replenish her. The overuse of the point-up pentagram is throwing the energies into space,causing a number of problems, and draining the earth of her ability to defend herself against these problems."
-Satan/Lucifer