I use 1745 Dankung tubes (traditional, black) with 10-12mm steel balls. I use 4 strands (1 loop on each side of the pouch, attaching to the slingshot 'ears').
These tubes are quite powerful, and they last a lot. They also give ample warning when they are wearing out (when the tubes are degrading they look softer, and the surface becomes irregular, wrinkled). After that, a small tear appears, but it progresses very slowly, it does not snap. I usually replace the tubes when the tear reaches 1/3 of the tube, to avoid issues. Usually the tubes wear first in the middle of the loop, where the rubber rubs the slingshot frame.
I should add that I don’t have much experience with flat bands or other tubes, but I am completely happy with the 1745 tubes.

36-rare rose wood hunting slingshot($53)

38($59)

40($59)