You are right about solo play being easier. Seems like I always end up with people in inferior gear, which makes killing stuff a lot harder! That and the extra damage and health granted the monsters.
I am a Witch doctor. Ya I read about the urn drop nerf, I have been farming Sarkoth, as he drops a good amount of gold, gems and blues, and he is very easy to kill. Between him, and the treasure goblin that often spawns in another cellar close by I can get about 5-7k per run, which takes about 3 minutes. Gets boring after a while though so maybe I will try out Warden and Butcher like you say!