Gonna go army, which is best?????????????

while i guess they are all similar, i wonder what one is the best choice?? 21e heavy construction equoment operator 4 to 12 wks ait. well wich is it 4 or12 wks? 21j general construction equipment operator 7 wks ait, or 21v concrete and asphalt equipment operator 4 to 12 wks ait?? HOWEVER, i am a little bit wary of picking any of these cause it says you will have to help be a combat engeneer. its that way with all of the 21 series. please help me