I was thinking about this like all day yesterday, and I'm going to say Ice/Light because everyone I ask said that fire/poison are strong, but it gets boring fast. Even though they are more powerful, for some reason everyone I asked said to be Ice/Light.
There was even a fire mage (on my way to orbis)that said if you want to have more fun, be ice/light.
It all depends on your kind of fighting style though, but I myself will become an Ice/Light mage once I get the opertunity.