What classes suck on harder difficulties?

[MPSchauster]

I have played a Barb to 10 and a WD to 17, just playing solo on normal mostly but would like to play on Inferno with my friends when I catch up to them.

That being said I was told WDs start to suck on harder difficulties. Any advice on what classes stay useful

[Chaosmage]

From my observation, degree of suckiness:

Monk > Witch Doctor > Barbarian > Wizard > Daemon Hunter

But it's relative, the Monk and the barbarian can be pretty good actually with decent gear, And the witch doctor does pretty well except there are only 2 viable attack skills for inferno (Zombie Bears and Poison Dart).
The DH is OP and the WIZ can get OP with good items.

In inferno it's normal to play along in a party with 3 DHs or 3 WIZs or 2 DH and a WIZ, etc... That speaks books.
There are about as many Barbarians as Witch Doctors, Monks are rare.

[MaxMax]

Monk > Witch Doctor > Barbarian > Wizard > Daemon Hunter

This seems correct. From experience, and what is being said around various "channels"

Haven't played WD yet, and my DH is only lvl16.
But for me wizard have been alot easier (than Monk & Barb) from act3 nightmare - where mobs start do actual damage.

[Valeli]

None really suck.... and you can be 100% positive that Blizzard is going to balance the classes anyways, so trying to pick one just based on power /today/ is a totally pointless endeavor at best, and counterproductive at worst.

For what it's worth, my HC DH, Wizard, and Barb have all done quite well for themselves into hell (none are in inferno yet, but that's being balanced and toned slightly too, so guessing how you'll work in it is another pointless endeavor).

[Kitteh]

I barb can solo act1/2 inferno with less then average gear for that time. Having said that, he doesn't solo them at the speed of light.