I made an interesting Excel Spreadsheet today. It uses
Effective Health theory to determine how much Effective Health is added by various types of buffs, potions, equipment upgrades, etc. It's specific to each character, but here's some of the numbers I came up with for my character. I assume that the target is a level 70 elite mob in all of the following calculations.
Commanding Shout -> 8.78% increase to EH
Ironshield Potion -> 11.18% increase to EH
Stoneshield Potion -> 8.95% increase to EH
Elixir of Superior Defense -> 2.01% increase to EH
Last Stand -> 30.00% increase to EH
Super Healing Potion -> 16% increase to EH
Heroic Potion -> 5.9% increase to EH
These are all when used by themselves and no other buffs active. Things change slightly when you have lots of other buffs. Let's say I have a Scroll of Protection V, Prayer of Fortitude, Commanding Shout, eating a Spicy Crawdad and an Elixir of Superior Defense.
Now the above numbers change to the following:
Ironshield Potion -> 13.16% increase to EH
Stoneshield Potion -> 10.53% increase to EH
Last Stand -> 36.56% increase to EH
Super Healing Potion -> 16.84% increase to EH
Heroic Potion -> 5.9% increase to EH
The ordering is still the same in that Super Healing Potion provides the largest boost to effective health. But by changing my stats via various buffs you can see the gap is closing. Ironshield Potion is only 3.5% behind Super Healing Potion when I'm buffed, vs. almost 5% behind a Super Healing Potion when unbuffed. So the answer may be different for you, it depends on your stats.