wow has 3 types of class imo:
all out attack (warrior, mage, rogue, hunter)
hybrid (shaman, paladin, druid, warlock)
all out defence (priest)
Its not as cut and dry as that by any means but it should give you an idea of what your after.
It is entirely dependent on your talent spending whether these apply to you or not.
I have a lvl 57 paladin and he bores the pants off me. He is too repetative. Also, once you turn lvl 40, you get your free horse but you become a bit lost. Platemail is useful but your not good enough to be primary tank, but also your heals are good but not good enough to be primary heal. Your stuck in the horrible off tank position, and due to the large number of palys, your going to be in lower demand for high level instances, and lower in the pecking order for phat loot. Imo they are the newby friendliest class.
A challenge class right now seems to either warlock or mage.
Im enjoying leveling my shaman right now, but I cant help wish i had rolled a priest.
Swings and roundabouts - and above all, this is just my opinion!