Not in my experience.
Armor absorbes 80% of damage delt, and only subtracts 66% from your total armor. (According to HL Wiki, and have noticed it myself.)
In english,
30 Armor
100 Health
Get hit and loses 30HP
Your armor drops down to 10
Your health drops down to 94 (thought normal zombs only did 5, lul)
So really, in the long run, armor is more effective than health (although not by much).
Get it now?