BH/Merc. Having your first companion be your healer along with being able to heal yourself easily puts the game on easy mode. Trash just dies, and while bosses take longer, you'll wear them down before you get into any real trouble.
The Sorceror is good at killing bosses, though... you still get healing even if you dump everything in Lightning or Madness. Crits are crits in this game. Same goes for BH, above. Your healer doesn't come for ages, so you need to be judicious about pulling in any extra trash or passers-by when you're generating a ton of lightning effects.
The Marauder used to have some really tough fights. Haven't touched mine in over a year, so they may have made some changes from 1.2~2.x to make things less "oh, wow, there is no challenge in this" and a minute later "OH MY GOD, I HATE THIS GAME, WHY ARE THEY SO MEAN". Annihilation was definitely a lot easier to live with than Carnage. You get a healer early, but the pet healers cannot keep up with damage spikes. They just fire off their crap in whatever order it's in. It's definitely worth considering going bio if you're going to bother with a profession, as the stims and medpacks are helpful.