I'm not really sure about it but don't stuns give hitmarkers and flashes don't? I have never really used flashes or whatever but thats what i've always thought. Anyway I always use stuns as an indicator of whether someone is there rather than to rush in and kill someone. I just use the hitmarker to know if they are there and then base my next move on that.
flashes show hitmarkers and if someone is in a place where there is less ground up high, using a flash is best to run up and shoot them instead of missing with a stun. besides, using the flash is better for campers. stun does nothing. the quicker animation is pointless and only good if youre rushing and used to quickness.