I hear ya, but I try to keep things simple;
First unit is a scout. 10 tib from WF, or 10-20 from barracks. This unit is built before y harv goes out to spot rushes, and to establish defenders advantage in the middle of the map.
Second unit is my vehicle counter from the same building. I don't want to have to build 1 unit, see a buggy/talon and have to swap buildings.
Next 3 are my strong anti-air,vehicle, and infantry counters. 1 for each type that I can rely on in the mid game to take on serious threats.
Lastly is my flavour spot. This is where I put the unit that my deck revolves around. For my NOD faction, it's stealth tanks. Sure, I've got my bikes for air and scorpions for ground, but Stealth tanks fit a niche roll and can do well. I don't build them every game, but I do often enough to be thankful I have them.
And there you go. My 4 step method to building strong decks =p