I play the game for high end in both PvE and PvP, always being opened minded to the options and abilities of other classes.

Mages just felt too squishy in Arena's, with the announced change for Iceblock being trainable makes a huge difference for it's viability. You can now be fire and actually contend.

For PvE any normal 5 man and most Heroics can be done with ease with the Shaman, I do not think this is possible with Mages.

I really enjoy the synergy Shamans offer. Mages also offer a lot to the table but I played a Mage for 2 years, was just time for change