I usually just build up my Ballistic and Viral defences and resistance, because Martial Artists can only punch you when your in IL with them and you'll be more worried about the hoards of hackers and gunners shooting you.
Also when I enter a mission area, I hit the gunners first as they have no shields and better damage out of IL, then I take out any hackers as they have good out of IL damage but you need to take their sheilds first then the MAs as they will spend the whole time shooting but down usually do as much damage and dont have as good accuracy... I can usually run into a normal mission with my MA alt and walk out the other end without needing a /sit break, but I have Direwolf (Increases health and health regen) and a few other helpful clothing. (Sakura Mask, Widow's Moor Shades both give good IS and Health Regen)
With Imposter Agents, you best off going with Ballistic resis and defence, that way they will hit less and when they do hit it will hurt less, though I stand by my Viral/Ballistic protection set for missions.