Sith Empire team's 5th slot: Assassin or Marauder?

I'm not so sure I'm ready to be so absolute about running Sith Trooper. ANd then deciding on 1 of the 2. I'm keeping this open and I'm going to see for myself what is working best with the mods I have. Does Taunt matter with fear? And the -def per ferocity. I'm not sure he's even a worthwhile fit. And against a mirror team, which we will be fighting, I'm not certain Sith trooper will be the best. I'm thinking that putting a fast 5 is going to be better than a fast 4. But it might be! I don't know. I'm going to play around a bit. I have 2 slots to fill between 3.