I think untill we see how hard will be later difficulties, it is impossible to say. Classes are well balanced, barb have highest HP, Monk have highesd dodge chance, WD have pets, DH and wiz stay on distance.But everything is a subject of balance, i don't think there will be a huge differences in farming speed.
Spamable seismic slam build.
constant buff from battle rage and war cry, reduced fury cost to seismic slam, very fast fury generation with reaping swing and leap attack, free AOE nuke every 105 seconds, and mobility+huge def bonus from iron impact
I have suspicion that there will be a certain areas, that will be impossible to pass without changing skills. Example - for bosses you will need mobility and defensive skills, and a single target DPS skill. It may be difficult to avoid a boss attack without a mobility skill, while for a larger packs of monsters you will need AOE dps, but i may be wrong.
Ganyo#2368
Spamable seismic slam build.
constant buff from battle rage and war cry, reduced fury cost to seismic slam, very fast fury generation with reaping swing and leap attack, free AOE nuke every 105 seconds, and mobility+huge def bonus from iron impact
http://us.battle.net/d3/en/calculator/barbarian#cgdYkT!YUS!babbba