[Suicide Junkie]

Well, the same thing can be said of early shields, too.

When deciding what to use, consider the Hitpoints per KT of space used.

For shields, this starts at 1.88 hp/kt, and rises to 9.38
Armor goes from 3 up to 5hp/kt
Organic armor has anywhere from 5hp/kt to 35 hp/kt depending on how the damage is applied during combat.

Also consider whether your opponent has phased weapons, in which case, anything below tech level 8 in shields will be weaker than armor.

Armor is cheaper to research at first, but the shield techs do go higher in the end.

You will also need to consider the bonuses given by Stealth Armor and Scattering armor. Although they are weaker than even normal armor, they both provide a stackable 15% defense bonus.
+30% to defense can make a huge difference in combat.