I've played all 5 characters through inferno and am now trying to farm keys on the higher monster powers.
Here are my views.
Everything is both build and coin purse dependent. If you play the "gold" way to steal a phrase from game of thrones the best character, I agree, is the WWBarb. That being said my WWbarb dies quite often on MP 5 even with the high life steal afforded to him. All my gear has good resist, high strength, I'm packing a 2M Skorn with only 1250 damage and but 5% life steal on top. what I cannot afford is similar or lower quality gear with decent vitality. I could build another MP7 witch doctor for the cost of upgrading one or two pieces currently. 25K life with the lifsteal of a WWbarb means my health goes from almost empty (if I'm lucky) to full and back again 10 times in the space of a single fight.
My top pick is the Witchdoctor. Since I earned things the "Iron" way refusing to put real dollars into the auction house. I have a solid zombie bears build which can easily do MP6 for farming. MP7 with some difficulty. I sniped some good deals but it probably cost me 15-20M to build. Gear for a 0Zombie dog build is so expensive you might as well forget about it. The witch doctor I find is a good blend of skills. Grasp of the dead allows for a degree of crowd control, even against elite and rare packs. Flaming skulls lets you long range single foes (how I managed to, slowly but surly, kill uber Magda and the skeleton king. Zombie bears is the main damage dealer and lets you take down large mobs or focus them on rare packs or elites and the fights don't go on for too long. Importantly it can be spammed (with good gear) before the attacking mob has a chance to land a single blow. Spirit walk has a rune that lets you do massive damage to any creature you pass through. With a weapon that does good life steal this can be used like a full restore, and can be used a couple times a fight, as well as breaking locking effects. The Gargantuan acts as a second meat shield, is tougher than the templar and has a power attack which usefully periodically stuns foes. Including act bosses and mini-bosses. All in all the witchdoctor isn't perfect against any one foe. But I have yet to run into a foe I couldn't take down without too much trouble using some combo of skills. (Without having to switch skills out)
Oh and haunt makes boss fights as you climb to 60 much much easier. Be warned though. The build tops out at MP8 unless you have bottomless pockets.
Honorable mention goes to CM wizards. I played archon wizard to level 60 but for inferno, especially since the latest patch where its monsters monsters everywhere you just need so much more crowd control then the wizard was previously capable of.
I've now built a decent CM wizard which made the jump from MP1 to MP5 quite smoothly I must say. Downside is the build is incredibly gear dependent. That being said the prices on CM wizard gear goes down each day. I probably geared mine for less than 5M
Downside of the CM wizard, it gets boring spamming 3 keys all the time, if you goof you die really fast, and most importantly some rare or elite packs possess affex combos which can give you a really bad time. If you hit a pack that does two of arcane enchanted, desecration, plagued, freezing, mortar or some like combo the place you need to stand for your blasts and freeze to hit are too close to the fire. Plus you can shoot your load on a single foe and be on cooldown as a pack approaches. Thats why I've seen CM wizards teleport away from lone white targets. It gets embarrassing how close one of those can come to bringing you down. Especially when you just laid a difficult rare pack low without any difficulty.
On the flip side CM wizards make the shortest work of reflect damage foes I've ever seen. (The bane of many other builds). And if you are patient enough they're the most pain free way to take down any boss, even diablo.
The monk build was the smoothest and fastest in terms of gameplay in my run to 60 and through inferno. Sweeping wind is vital. Its a shame the life regen 1/2 the skills incorporate doesn't scale well. I'd need to gear up to go above MP3 at the moment. The cost of improvement gear, like a good Nats ring surprisingly costs more than gearing my CM wizard from scratch did.
And then there is the Demon hunter. Pre patch 1.05 before monster power was a thing Demon hunter was by far my favorite. Really easy kiting. Fullscreen attack with a solid spammable area kill. Now my Demon Hunter is simply no good anymore. On the higher monster powers it will take you longer to kill rare or elite packs. Period. Demon hunters are made of paper. Kite all you want with more mobs and packs not going down as fast you're in permanent retreat. You either take the elite pack down before you get cornered and die or you don't. I could invest heavy in gear but I won't because ultimately I don't think it'll make a difference if I get cornered and die in one hit or two
-Hope it helps