In my opinion it completely depends on play style. I myself max out swords and archers, with a few points in Magikill and just play a survival game to starve out my AI opponent. Eventually their gold supplies get so far out from their base that my eco catches up on its own, and before that time all I have to do is drag out the fighting.
I don't tend to buy Spears because in my opinion they need far too many upgrades to be useful.
I myself prefer kiting all day with swords and just stalling the match in the middle of the field. I go for the push when my opponent fall on their knees from running out of resources. On insane its frustrating with every arrow 1-hit-KO-ing my Swordwrath but I still find it fun.
A friend of mine just plays mainly with Spears, and I've tried games spamming Magikill. All comes down to what sort of game you want to play really.