Mages are excellent in WSG if you know how to play them. I have a few links here of good 19 mages.

Alliance
http://wowarmory.com/character-sheet.xml?r=Uldum&n=Shoopdawoopa

http://wowarmory.com/character-sheet.xml?r=Crushridge&n=Icicles

Horde
http://wowarmory.com/character-sheet.xml?r=Bronzebeard&n=Plumeria

http://wowarmory.com/character-sheet.xml?r=Bronzebeard&n=Di%C3%A5