A high strength nylon weave fabric single point bungee sling with metal spring-loaded attachment clip.
The two-point sling arrangement is arguably the least convoluted sling-theory option; clipping to the front and rear of your weapon, it can sling over your shoulder in the style of an old fashioned rifleman. The elasticated lower portion makes it more comfortable on your shoulders as it helps to reduce the shock impulse when bearing a load which has a habit of moving around with alot of force.
In terms of criticisms, the leading nag about two point slings is that using the sling and shooting the gun are practically two different stances. Either carry on your shoulder or shoulder it to fire, you have to either take it off or put it back on to switch between carry styles.
The two-point sling is great for moving around non-hostile zones, taking all the weight on to your shoulder and off your hands but its a bit fiddly to react to opposition forces if they catch you unaware. The two point sling is a particularly appropriate option for longer weapons which are not otherwise appropriate for single point slings.
Two point slings are great but if your looking to sacrifice carry load relief for speed and agility then be sure to check out single point slings as well.