Soldato
I'm still stuck on N'erud, that's where it sent me after i re-rolled down to the medium difficulty. I have finally bought and switched archetypes to the dog so solo has got a bit easier, I just send the dog in and pick them off with the hunter rifle. got a decent smg pistol for when I need a short range weapon too.
I think the Handler with mutt is the game's intended solo character for what is essentially a co-op game.