Probably gonna be a 48 hour maintenance lol

No one really knows which classes have the highest dps right now or maybe even halfway through Cata. Things change a lot throughout the patches. I would advise playing a class that you find interesting because it will be the interest for your character that keeps you going from level 1 - 84 and not burning out halfway while leveling till 85, which is where the real game begins.

I suppose you prefer damage dealing classes since you talk about highest attack. In WoW, damage dealers are often refered to as DPS meaning Damage per second. You might want to start off with a range type DPS, I think it is easier to handle although most of my characters are melee.

Range dps classes:
Mage - They call it the "Glass cannon'. Fire, Ice and Arcane specialities
Warlock - Shadow damage, summon creatures.. Evil stuff
Druid (Moonkin) - Looks like an Owl + Bear. Uses nature magic.
Hunter - Arrows and pets
Shaman (Elemental) - Nature magic. Totems (gives buffs) can be slightly annoying or interesting (depends on you)
Priest (Shadow) - Shadow damage. Heals party and provides mana rejuv while damaging enemy.

Not sure if I have left any out, should be it.