It depends on your objectives.
Do you want a good score? Open top Kydex on the belt is the large majority choice. My most used guns have streaks in the blue from where they rub on the draw and there is even a little burnishing on my one stainless gun. Yawn.

Do you want to exercise your carry rig with IWB? Nothing wrong with that as long as the equipment and technique allow safe holstering and draw.