I'm not sure if this is helpful, but I always, and logically, make my squad captains the highest military-skilled individual in the bunch. I don't know if that actually does that much.
Now listen. The squad captain/commander is THE MOST IMPORTANT GUY IN THE WORLD.
My last fortress had some migrant as militia commander. Sure she had good military skills. But she was "put off by autority and tradition", "dislikes contracts and regulations", plus the damned "She is extremely cautious".
That combined to poor body shape (just "mighty", "tough", "slow to tire", nothing about agility) get her last to the move order location, regardless of her legendary statuses, professionnal armor user and expert observer.
Now suppose the caravan to protect MOVE. I have to give a NEW move order! But who tells my soldiers to adjust and station there? The freakin militia commander, who, it happens, barely sees its squad members over the horizon, much less aknowledges the new order and just walk, yes WALK, to the middle of the desert with NO CARAVAN IN SIGHT!
My current fort has another migrant as militia commander. Despite being "unassertive" and "occasionally given to procrastination", she's always first or barely second at the combat scenes, she spots ennemies and pwn them while others just return to barracks, all thanks to very nice body shape, skills and a sense of duty.
My conclusion : Give squad command to the dwarf arriving first at combat. Soldiers will follow him, and he will react faster to orders.
Your thoughts?