Engineer, as most of sm's are escorting missions.
Shock is in no way a proper ship for missions anywhere. You need to be very familiar with Shock to be able to play sm's with it. Works well on Vega & Antares, but thats it.
It is more a pvp based ship.
Alternative to Engineer and sm's would be a Storm or Tank.
But after all the choice depends of yourself, your skill to play, experience with different type of ships, and the way you play.
For best survival for yourself but not npc's would then be Tank, it is a defensive ship with strong armor.
Storm would be a class with lots of firepower, you can defend npc's with it, but no guaranty of survival of them. Best for grinding.
Engineer will keep the npc's safe, and also yourself. The stun from commanders or other will not stun when Protection shield is up, but don't forget, they can as well stun the ones you are escorting, so make a wise choice, protection for you or for escorted, mission will fail if npc dies, but might also fail if you die. lol ^^