It doesn't matter. i purposely put my lowest % player as penalty, freekick, corner & captain because the game recognize the best player to take em all compare to your choosing.
The best part is when u usually see this 1 guy take fk but somehow other player takes it u instantly know it's a goal and sometimes when this frequent setpiece taker have a bad day u just sub him out and the 2nd best player game recognize will probably do setpiece better than the 1st 1.
So when i put this lousy reserve player as captain, the game will automatically put the best candidate as captain on field. but luckily we have no idea who they're because it isn't available to see C in the pitch.
Oh if u guys wondering & asking "then why not just leave the setpiece, captain empty as is..?"
well if u do that, your team preparation will be lower and cant get superb preparation.
so i just put whichever player that isn't in matchday squad as the captain..