I don't know. I put a shield and medical generator at a slight LOS from the enemy mob and throw down a phaser turret for good measure and I'm well nigh invincible, at least in PvE. For some reason, mobs attack the turrets first, even though they throw off the least dps (at least in my experience). They seem to hold their own against everything except plasma grenades.
Well I was speaking of engy skills, not kits. That is, the skills you get with your engy captain while leveling up.