Hello, Athri here.
I'll have to say that my favorite class is the Mage.
I'll usually play an Undead Mage, mostly because the Will of the Forsaken attribute to me is really in my opinion, the best racial in the game
I like the class alot for the challenge that it gives me towards different classes.
For example, rogues.
To beat a rogue as a mage, you would need some very nice timing skills, and ways to not let yourself get stun-locked by them.
Usually, the Frost Elemental is your best friend in fights versus Rogues. So is Ice Block.
You would usually need a Medallion or Insignia of the Horde on fights versus rogues, to get away from blind.
Mage versus Paladin duels are also very fun, since you have to watch out if the paladin is retribution.
These duels are alot harder if you're not frost or frost/arcane.
Reason being because fire doesn't have Ice Barrier, which is a GREAT spell do absorb some of the tremendous damage that Paladins can do in a short amount of time.
Although, even if you are frost, the Blessing of Freedom paladins can do is very troublesome. It's strongly recommended to SpellSteal as SOON as you see that blessing on the paladin. Trinket out of Repentance, and Blink out of Hammer of Justice.
That's just some of the reasons I like being a mage the best.
Edit: With the new talents implemented in Wrath of the Lich King, one of the really great ones is "Shattered Barrier". That will greatly help mages flee from hard opponents. Brain Freeze Is a GREAT way to do some INCREDIBLE burst damage on a target. Imagine casting a frostbolt and then being able to cast an instant cast fireball that doesn't cost mana. That's sort of like a giant Ice Lance, am I right? Imagine one of those while you have 1500+ spell damage?
I can't wait.
~Athri.