Defenitely warrior specc dual wield. Right now I reached lvl 42 and rush attack (15) combined with battle rage (15) did a 20000 crit and I'm sure it can go a lot higher if I cap Heightned Reflex (right now it's on 58%).
My build is
-> 15 Whirlwind
-> 15 Rush Attack
-> 15 Battle Rage
-> 13 Dual Wield Spec
-> 15 Bleed
And some in Life Leech for the heals
While leveling up the priority on these Skills are defenitely
1) Dual Wield Spec
2) Battle Rage
3) Have 1 point in Rush Attack (I personally only invested the 14 points to make it imba after lvl40 and only when DW, BR, WW and Bleed were caped)
4) Whirlwind (for 360° aoe and push back at 15 it's only 1sec cool down!)
5) Bleed
6) Deathblow (don't put points here until the rest is caped)
7) Reflect (don't waste points on this at all is my advice)
I keep BR on and only use RA and WW as specials rest are normal attacks (good old hack and slash) I haven't tried out Thousand Strikes yet I'm getting soon 5 points from the Viper Armor so I might boost that skill up next and try it.
As for the rest of the skills 1 in Evade and 1 in Healing is Very good for leveling so get them early in the game. Also I use 1 point in Mana leach, this way my mana is always full.
I have 15 in mindread cause I want to know everyone's secret for free but use that only when starting the Flames of Vengeance in Aleroth (the mind reading there is quite expensive so it's worth it)
Always keep Lockpicking caped cause it's frustrating losing the extra loot. You can get it to 7 in Aleroth by mindreading people in Bandit cave (next to playhouse) and using the female trainer at the ministery.
I didn't tried any other specc yet and I'm curious about ranger maybe the game might be harder... I'm in nightmare mode and honestly I'm disapointed in most of the fights. I really thought Ba'al would be an hard encounter but it dies in 3-4 blows in the hardest mode with this specc. I hope the battle against Damien will be more intense
Hope it helps!