Opinion time! :)
So, lets say you're playing on a largish map, and your opponent is turtleing for the center. (Basic turtle strat- spears up front, archers in the back) Now, you just happen to have a magikill, and your opponent realizes this. He sends his spears after your magikill, so you only have time for one spell. Should you A) Poison the speartons or B) Blow up the archidons?