Arcane. If you're one of those people that cares about damage and nothing else, of course.
Right, as the world goes, is only in question between equals in power, while the strong do what they can and the weak suffer what they must.
- Thucydides
There is a modern myth that people have always tended towards democracy, constitutions, electoral rights; but in truth, love of freedom has never been the predominant note of popular politics. At most times, popular demand has been for a strong government.
If you are interested in serious raiding, Arcane is the stronger spec at the moment. If you like to spend your time just doing dailies, looking for raid or just killing things for fun, both fire and frost are very fun to play with.
I personally use Fire for everything included raiding but my Mage was born and raised as a pyromaniac. You can try all three to see what is best for you....
If you like mashing one button all-day every-day, then Arcane is the spec for you! If you like mobility, choose Frost. If you like a challenge, choose Fire. It's all about personal preference.