My first class was IA Operative, healing spec, then a BH Merc, healing again (which seemed like a breeze after agent). And after that SW Juggernaut, immortal spec. With Quinn companion its way too easy. Takes long most of the time, but I am quite unbreakable. Only have to use defensive skills if I'm in fights with golds, bosses or too many small stuff.
I'm not sure about marauders, I've seen them hit hard compared to me, but juggernaut feels rather solid. I'm only lvl 35 on him and just landed on Quesh, but I soloed every class quest before (mostly on first try) and the only thing I had trouble with was the fight against 2 silver jedi on tatooine when my companion was knocked out. But I was 2 levels lower than recommended level.