The standard class which I find the most effective and capable of surviving Hardcore is the new Death Knight. The status effects that decrease your maximum mana are awesome, and his multiple debuffs on hit add up. All of those come on top of the very solid two-handed and sword/axe masteries.
The most devastating straight melee damage dealer is the Weaponmaster/Blackguard. He is a glass cannon, but he can easily one-shot anything that comes close. He is absolutely straightforward - four masteries that enhance your two-handed sword, and pick two skills to kill with - one single target and one for mobs.
The safest character I've used is a Defender/Magician. Rock solid defense - plate armor, shield that can be used with a wand, three defense skills, and a defense multiplier skill. Then you have a damage shield, a teleport for getting out of tight spot, and the arcane barrage that is devastating as long as you choose you terrain and kill from afar.
I play only hardcore, so I only play characters that either have solid defense or kill quickly enough to keep safe. There are much better glass cannons, but those will die through no fault of their own, sometimes.
No good deed goes unpunished...