I think Myth has some really cool spells. However, it takes quite a while to receive the powerful spells, like Basilisk. Fire spells are pretty powerful from the start. I think it would be easier to win a battle with Fire, especially if you are on lower levels.
Honestly, Myth stands out because of minions. Unless you somehow get Talos at a very early level (Dragonspyre, Mooshu) You're not going to beat the game. The minions become useless.
So- start with fire. Myth's awesome too, though, I find it very fun (Quite possibly because I have a habit of naming my spells.) and it's also very nice in PvP.