I guess I'm showing my military past, here, but for my money, the U.S. standard cotton web sling meets all of my needs. Easy to adjust, wide enough for comfortable carry, can make a "hasty sling" in an instant, and a target sling in but a few moments. On sporting rifles, I dispense with the metal clip that terminates it at one end because it rattles (I used to do this on my issued military arms as well, because I never understood alerting the enemy to one's presence). With QD sling swivels, there's no disadvantage to doing this. OK, it's not the most beautiful sling in the world, but it's sure one of the most practical for nearly all purposes. Here's a couple on an M1 and an M14. The M1 has a WWII issue sling, while the M14 has one from more current stocks.
