If you want to make money, go Skinning and Herbalism.
Tauren Warriors get 5% more Health and War Stomp, so I consider them the best warriors.
Trolls used to be the best Shamans, before they nerfed us

(Took away our +10% mana regeneration)
My friend is an Orc Hunter and he's one hell of a PvPer, as well as a great soloer, because his pet can tank. I have to say, though, before he outleveled me, I kicked his ass 1v1.
Shamans are a little bit rigged. Honestly, I think it'd be fair if they just took away our quikc-heal, but whatever. Even though they nerfed us, being a Troll allows me to be one hell of a healer. Priests aren't neccesary when I'm in a party, plus I can bring myself back to life once per hour, which is really handy when we wipe in and instance. If you plan on being a tank, Tauren is the best Shaman, though you will miss out on a big lot of mana. I wouldn't suggest Orc for anything but Warlock and Hunter, but it's really your preference. Undead have the best racials in the game, but they can't be Shamans
Warlocks = Very complicated, but very good
Mages = Complicated, and great support units. Not good soloers
Warriors = Damage takers. Period.
Hunters = Best soloers by far, good PvP
Shamans = Think a Mage, Warrior, and Priest in one
Druids = Jack of all Trades class
Priest = Best healers (duh), but Undead ones get great offensive spells as well
Of course, Engineering is the best profession.
Engineers can:
Make and use Grenades (Excellent for when you're out of mana)
Make and use combat pets
Mind control people (Usually a priest and warlock only thing)
Make priest shield devices
Make shrink rays and discombobulators (Great Debuffs)
Make and use the Death Ray (Crits for 4K)
Make and use invisibility devices
Make one of the best guns and best shields in the game (much later in)
Engineers own all.

ADDITION:
First aid is great, too, if you're a non-healing class.