Hmm, to be honest i had a hard time as DRK between lvl 30 - 35 <--> after grit & darkside - before blood price.
I had good time as gladiator as well, fun class for <50 lvl duns.
I had good time also as marauder (with invigorate as cross class), and later warrior with defiance.

I quess thats it. DRK 30-35 was rather though for this early leveling.