It's worth noting that webbing slings degrade very quickly, and lose as much as 60% of their strength over a year or two. The reason is that 100% of the load bearing fibre is on the exterior surface, so it gets loaded with grit, abraded etc. It should also be noted that webbing slings are often rated to their breaking strain, not their working load limit. Make sure which yours is rated to. If it is rated to its breaking strain, for example, 2,000 lbs, then the safe working load of that sling will be approximately 1/5 of that figure, or 400lbs. If you are using it for heavy rigging and shock loading it, then the safe working load will only be 1/10 of its breaking strain, or around 200lbs.
By contrast, rigging slings (also called crane slings) have all the load bearing fibres on the inside of a protective sheath. They degrade very little, and are rated to their safe working load ie. a 2,200lb rigging sling will actually have a breaking strain of 11,000lbs. They are also very cheap, you can pick up a 2,200lb rigging sling for about $5.
Whoopie slings are good.