Starcraft – Are shield upgrades more effective than armor upgrades

The short answer is no.

There is an important trade off between shield and armor. Obviously shield upgrades affect more units (air and ground), but beyond that, shield regenerate so they often prevent damage more than once. By comparison units often have less shields than health. There is also a cost difference between the two.

edit: It is important to note that pro level Protoss players (ie. tester) often choose armor over shields. The reason for this, is that in a large battle, the higher amount of HP usually means that armor will have a large effect during the course of the battle, additionally, EMP dictates that Protoss are often less able to rely on their shields in TvP.

It sounds like you're building a large army and using it to gain map control, but then are falling prey to things like drops and backdooring.

If you have map control your first thought should never be: Crush my opponent, as you're essentially sacrificing an advantage (map control) for an unsure victory (because he doesn't control the map doesn't mean he can't take you). Instead your thought should be: take the map. I think you'll find this change in philosophy will lead to situations where you have a much more powerful economy than him and you're able to kill him with attrition.

Now if you're falling prey to things like BD here is a quick check list for you:

• Are you scouting? an Observer should be the first thing you build out of Robo. If you don't go Robo, a Hallucination works just as well. Sometimes scouting means sacrificing some Zealots in a pointless charge to just get inside his base.
• If you're scouting, are you seeing it coming? Overlords on the edge of your base, Starport with Reactor + 3 Rax, all of these are indicative of certain strategies you should watch out for.
• If you see it coming, how are you responding? If you have map control that means you should be able to respond quickly. Shutting down these back door attempts is often a bigger victory than a straight up conflict
• Finally, Do you have map control? If you don't have map control that means he does, and if he's beating you with map control then your problem is not "how do I deal with a base trade?" but rather, how do I regain the advantage.