Maybe depends on what you like... We enjoy a little metallic grain to the sound, some presence instead of dullness, and also we used an E-string tuned down to B, instead of a real B-string at B, just to get it even more in that direction...
But if you want a flatter, "warmer" sound, that doesn't sting as much, I'm sure you can use anything from old strings to rubber bands. But we want the bass to be heard not only felt.