Heya,

From my (very limited) experience, fastest way to level is with a 2H weapon, it's just flat out broken.

Get Flight of Gav (Can't remember the whole name), put everything into either Ferocity for Crit or Toughness for tankiness.
Get either Hammer or Cyclone or Bleeding Edge - all three skill ridiculously well with a 2H.

For reference sake, I played dual wield, my damage was as followed;
Dagger + Sword = Around 850dps
Just Dagger = Around 820dps
Dagger + Dagger = Around 400dps (This has to be a bug tho...)

My friend played 2H and his damage was around 2k DPS.

Both of us had pretty trashy gear, granted. And we both sucks when it came to building our characters - However, we went almost the same paths in the passive tree, major difference is I picked Merciless.

So Tl:dr - Get 2H and focus on either Toughness or Ferocity.

Hope this helps.