the residue in scotch tape is bad for the screen, if u use it regularly, the screen is probably not as smooth as without using it.
the best way to use microfiber, especially the one that u got when u buy an iMac. it's very smooth and high quality.
when u clean the screen using microfiber or your cotton tshirt, make sure to rub it without any pressure at first so if there is a big dirt and dust, it will go away first, so the second time u rub it, this time apply pressure.
dont go rub the screen with pressure the first time, because dirt and dust that might scratch the coating or even the screen.