A few objective truths I've found at all ages for throw-ins:

when playing someone's feet, really hard, flat throw-ins (I call them 'bullets') are usually easier to control than a soft, looping one
almost every team defends throw-ins by man-marking
except for the first and last ~20 yards of the field, you can usually use the same set of movements/options for the thrower
teams never mark the guy taking the throw, so if you can find a way to incorporate them, you can find some time on the ball (I stole that from a Cruyff quote)
because it's a restart, the offensive team controls the timing