First off, I know I’m late to reply. Secondly, I’m not addressing any PvP aspect because the game will be changed before we get to smash each other, sadly. Thirdly, this is my opinion after the playing the beta and reading multiple posts from blizzard (and gamers) which fanned my increasing hunger for this game.
So with that being said, I believe the barbarian will be the first class to be able to complete inferno (unless blizzard failed miserably at making the game difficult). The armor, multiple mobility abilities, life gaining abilities and being able to switch between two weapons and a shield in combat greatly increase his chances. Yes the wizards can use every form of damage besides the monks’ holy damage, yes witch doctors get pets (that will probably get one shotted) on a 60 second cool down, yes demon hunters get a 15% speed increase with unlimited ranged attacks but all other classes cannot compete with a geared barbarian. A 30% chance to activate revenge (with provocation) means that if you stack armor and mainly vitality (since it’s a 5% heal, not a numeric value) you become an amazing healer for yourself, and luckily most enemies in Diablo have always ran to you. Ranged enemies will get the brunt of leap, furious charge, sprint, ancient spear or my favorite weapon throw with dread bomb rune (thrown corpses ftw). Unfortunately, since every level 60 barbarian will be the exact same as every other level 60 barbarian naked it will all come down to gear and those 19,683 gems you will have to pick up for one radiant star amethyst (http://www.diablo3artisans.com/jewelcrafting/gem-calculator/ ) with an 18% increase to vitality in a helm.