For everyone's on Twitter's answers to this question (in 140 characters or less) -- or to add your own (in as many characters as you'd like) -- read on!
gnomeangel @WoWInsider Fastest Levelers = Hunters. It's practically cheating! U always have 2 in your party = harder 2 die = more time 2 level. Luv it!
mattycallen @WoWInsider paladin. Easy to solo and manage multiple mobs.
toniou @WoWInsider warrior is fastest - if you have a healer tagged along, as they are unstoppable then. ;)
OhCapital @WoWInsider probably rogue since you can stealth past trash for most fetch missions and these days there are more than enough quests
caryy @wowinsider Blood Death Knight. No downtime. If we're starting at 1, probably Hunter.
Janubris @WoWInsider a death knight, if they have a lvl 55+ toon. Druids and hunters are good too. There is basically no down time for these classes.
ErrorJustin @WoWInsider Warlock! All you have to do is dot up 8 mobs then run around. They'll all die at your feet.
RonnyBelmont @WoWInsider A hunter don't take dmg + Aspect of Viper + Healing pet during combat (no/less downtime). Also twice the dmg on mobs (You + pet)
jaminbee_007 @WoWInsider the warlock, pets and dots, just hit and run, litterally, that or the DK, it starts at 55, lol. other class would be hunter, pet
VSUReaper @WoWInsider Prot warrior 70-80. Less downtime w/ right gear, lots of aoe killing.
us3rX @Wowinsider a druid. simply cause everyone needs a healer, tank or dps. A druid can do them all. XD
adamjamess @WoWInsider easily warlock or hunter. Mainly because of the pet. I'de also venture to say druid, esp. feral, little downtime/very versatile
tahoepenguin @WoWInsider death knight because it's so easy to gain health back simultaneously while fighting even mobs
cristolmer @WoWInsider druid is the fastest to level after cat form. I don't know why haha, but I've leveled every class and it was fastest
chrisboozer @WoWInsider IMO Druid is the fastest class to level past level 20 simply because ur offensive & healing abilities dont use the same resource
Quantumhair @WoWInsider Gonna have to go with DK for obvious reasons
gjhsu @WoWInsider Rogues or hunter, imo. I found leveling quite easy on my rogue. Can sneak around most roadblocks, stunlocks, etc. ezmode
cjivan @WoWInsider Feral Druid was super easy to level. There's 0 downtime. You can heal, tank, dps, all without stopping to eat or regen mana.
crayzeigh @WoWInsider Death Knight. Or does that not count? Starting 55 levels into the game is a pretty big help.
leafshine @WoWInsider Not resto druids. REALLY not resto druids.
DanielEfton @WoWInsider it doesn't matter what the fastest to level is for any number of people. if you enjoy it it will fly by. experiment!
mattycus @WoWInsider Holy Priest levels the fastest if you're Matticus!
turtyl @WoWInsider Fastest class to level: Death Knight. AOE grinding, absolutely no downtime. Otherwise, Warlock, for the same reason.
Shooresh @wowinsider I would say feral druid simply because of the versatility and endurance which coupled with a sound levelling strategy
mindflayer @WoWInsider Fastest classes to level are hunter and Warlock, as they have always been. That said, the Death Knight starts at level 55.
CultClassic @WoWInsider Definitely hunter. With a good tenacity pet, Beastmastery (even now, ugh) can give you a free tank, and mendpet lets you heal.
Kadomi @WoWInsider BM hunters, no question. Probably also the most boring to level, but I am terribly biased. ;)
nesukun @WoWInsider probably warlocks or huters, low downtime, pet, AOE capable. both are well known as leveling machines.
Fallakin @WoWInsider Warlock. 1-40 is pretty much Corruption, Immolate, SB, Fear rinse repeat. At 40 you get Dark Pact and never have to stop.
BruceMri @WoWInsider Right now, death knight; no mana, tough, escape options, and lots of damage.
FrakTruck @wowinsider hunter is the easiest by far, but the fastest has to be rogue
kombatmedik @WoWInsider NOT. PALADIN.
coreycubed @WoWInsider thanks. I'm pretty sure hunter still wins that contest, pet spam + heirloom shoulders, bow = fast XP. add RAF and you're golden!
Spoonwolf @WoWInsider enhancement shaman. I never run out of mana, I self heal, I can tank most group quests with wolves or totem and I can self rez.
Draco2869 @WoWInsider Starting from lvl 1 think it would be warrior, always can find a group to run instances which equals lots of exp
mew7265 @WoWInsider hunters because you've got a pet who can tank mobs thus keeping you alive to kill mobs faster.
themightysven @WoWinsider Paladin, with seal of wisdom, and judge of light keeps me full up, no need for food/moonberry juice
necroscopic @WoWInsider I think the hunter still has the title, since its WOW with training wheels. The pet can take one mob, and you can take another.
Tensai @WoWInsider Hunter. Gorilladin + Volley (even with the nerf) is one of the earliest and strongest AoE combos for any class.
seanlacey @wowinsider for 1-80 has to be hunters.
seanlacey @WoWInsider Death Knights, besides the obvious of starting at 55 they have great aoe ability and the fastest class to level through outland
dadexter @WoWInsider Warlock, because of the pet, and the cool factor.
jaxor @WoWInsider Locks & Hunters- you get assistants and can just pound away once you find the groove where you don't pull every other attack
acedanger @wowinsider hunters are fastest b/c you have tank heals and dps all rolled into one lil awesome pet (go BM!!)
varmazis @WoWInsider dunno, but it definitely ISN'T priests (including shadow).
jacobovillegas @WoWInsider Warlocks and Hunters Imo. Having a pet and CC it's a huge advantage.
Greg4cr @WoWInsider hunter, easiest to solo.
caniki @WoWInsider Hunter. Always having a tank and being able to heal it is phenomenal.
massive_unfocus @WoWInsider Does DK count? 'cos technically that's the fastest 55 levels. ;) Seriously though, pretty quick to level full stop.
dickiemaxx @WoWInsider hunter is the easiest class to level your pet keeps you alive. No deaths = faster leveling.
mychilli @WoWInsider Hunters or warlocks, for pet tanks :) Or maybe a druid
Arrens @WoWInsider Warlock or Hunter. It's easier with a pet to hold aggro.
GuillaumeCL @WoWInsider Hunter, pet on aggressive, alt+tab. Or feral druid, no downtime.
agobelle @WoWInsider if he's a newbie to wow: Hunter. If he's a seasoned wow player: Mage. Both are excellent for fast kills & grinds despite nerf.
midzilla @WoWInsider Paladin. 16-80 in a month, mostly as prot. The ability to run into groups of mobs and walk out with completed quests and EXP.
dechion @WoWInsider The fastest I have managed to level with was a BM specced hunter using a tenacity pet.
stoppableforce @WoWInsider BM hunter, after level 10. Stopping to rest is for wusses.
dadexter @WoWInsider Death Knights don't count, right? :P
jamessocol @WoWInsider My hunter is going fast, but maybe because I've done all the quests before.