Best way to do upgrades against Zerg

Obviously each race is a little different, Armour/Shield upgrades not great versus Protoss.
Shield isn’t effective vs Terran but in a PvZ once you get +2 with weapons and you have your second forge by then is it better to go +3-+1 or +2+1+1 but have it 50s faster, then follow up with +3+2+1?