Are we talking high level or low level gameplay? It really does matter. If we’re talking high level, blizzard hands down. A bunch of skull towers are NOT fun to fight against without blizzard in your arsenal, especially if the person you are raiding has all of them maxed out. Second I would take Swordrain, because maxed arblasters partnered with maxed cannons (both boosted) can do serious damage across lanes. Hammerstrike can’t reach them, so your troops will be in serious trouble, even if you stay with them to keep them alive; all the while wasting precious time. With Swordrain/Blizzard combo, this isn’t a huge issue. Use a blizzard first, THEN swordrain. If you swordrain first, you will kill the arbs, and they will heal the cannons and everything else around them. With blizzard you can also hit the skull tower that is probably in the next lane raining down on you. The range on both of these seriously can’t be beat. Last is hammerstrike.
If we’re talking at a lower level, first is hammerstrike, swordrain, then blizzard. I say blizzard last because at a lower level, you don’t have to worry about an army of maxed skull towers standing in your way. Raiding with froster and an ice type weapon/glove will give you all of the slowing you will need. At a lower level, you will probably see many more snake towers, in which case hammerstrike will serve well. Partnered with your cannons, you won’t have much trouble. I say swordrain second simply because it’s range and damage allows it to kill any piercing typed dps. I am assuming that all troops arent maxed, since we are talking about lower level gameplay.