My tests indicated the better free-kick/penalty takers are those with both high Shooting and Finishing %, even if the finishing is a 'grey' skill (for MR). If they have an appropriate SA (Free-kick, Penalty kick, Shadow striker or 1-on-1 finisher) then the better.
ST with Corner-kick are rubbish at corners, I tend to use DL/DR with high Crossing %, again, if they have the appropriate SA, then the better.