In my opinion mage is the best for farming gold and leveling, if you have a mage follow the steps and you can get over 20g in an hour at level 28:
1- make sure your mage is 28+ and frost spec with imp blizzard....ice block and ice barrier arnt needed but help alot.
2- find a nice grinding spot with no spellcasters or ranged mobs.
3- put all buffs on except the armor buff.
4- put on mana sheild or ice barrier if you have it.
5- run arround your sellected grinding spot, agroe everything, if u get dazed then blink, if you have a mount then agroe all of them with your mount. (optional: to keep agroe on you and off someone else just keep doing arcane explosion rank 1)
6- when you have all mobs on you, dismount or stop running, ice block if you have it, if not then just frost nova straight away, if you have ice block then get out of it frost nova and blink.
7- make sure you are in a good distance to start channeling blizzard.
8- you should be able to do two blizzards until they get to you, your frost nove should be out of cd, use it. at this point your mana might be done so go ahead and use evocation.
9- do steps 7 and 8 again but dont frost nova at the end... instead cone of cold and spam arcane explosion (your highest rank).
10- before doing this make sure you have hp pots, if you dont have a mount swiftness pot helps to agroe mobs.
there you go 10 easy steps to follow!
enjoy the gold and the xp.