Two red and apocalyptic one-man armies. Zero wins and Tirek splits, HANDS DOWN. (The Raven vs Twilight video revealed that the FiM universe isn’t so invincible after all.)  
-Zero is far more skilled than both Twilight and Tirek.  
-Zero regularly fights far more skilled enemies than both Twilight and Tirek ever have.  
-Zero survived the fall of Eurasia, which was as strong as the asteroid impact that wiped out the dinosaurs (equivalent to 100,000,000,000,000 tons of TNT. The biggest explosion Twilight and Tirek caused during their first fight was microscopic in comparison.) Mind you, this is BASE FORM Zero!  
-By having no magic to drain, Zero nullifies Tirek’s greatest asset.  
-Zero killed Dr. Weil, who survived a shot from a city-destroying laser satellite none the worse for wear.  
-Zero can counter Quick Man-level speeds (and stop time with Dark Hold).  
-For Zero, giant enemies are Tuesday.