This was a challenging topic to research.  One of the best sources was a caving and vertical rescue article that was recently pulled from the internet - bummer.  Fortunately, I found another less comprehensive source: Article on Rope/Knot Strength.  Let's take a closer look at our most common rescue knots:

• Figure Eight Family: Strength 80%.  This is a climbers and rescue workers first choice due to strength, ease of tying, and easy to inspect.  It is also a very versatile set of knots.
• Bowline: Strength 60%.  If you use this knot, add a backing knot so it will not come undone.  This knot is easy to tie one-handed.  Once stressed, it can be difficult to untie.  In general, we prefer the Figure Eight Loop instead.  The Bowlinwe is no longer in the SWR Curriculum.
• Water Knot: Strength 64%.  This is an exceptionally good know when working with webbing instead of rope.  It is very easy to inspect.  Make certain you leave plenty of tail, as much as 3".
• Tensionless Hitch: Strength 100%.  Friction and a very gradual bend are the keys to this knot.  It is also very easy to untie.
• Alpine/Butterfly: Strength 75%.  A very effective knot for a 90 ° pull.  When used to bypass a rope defect, strength is 57%.
• Round Turn with Two Half Hitches: Strength 75%.  This is a self tightening knot and a far better choice than the clove hitch which can easily slip.
• Double Fisherman Knot: Strength 68%.  We use the double (or tripple) fisherman knot to tie our Prussic Loops.  This is a very smooth knot that doesn't slip.  It is also one of the strongest knots for tying two ropes together.
• Prussic Hitch: Strength varies.  Actually this knot is meant to be the weaker part of the system.  The prussic Loop fails by slipping along the larger rope giving us a warning sign to back off immediately.  This is an important safety feature in mechanical advantage systems.