Another fan of the ladder type rubber rail covers. Preferred as mentioned, where the support hand meets the rail, easy on hands and allows easy grip. Also easy to put on/off whereas others are more tedious(Magpul XTM, Larue clips).
For full panels, I find lots of them add lots of bulk in areas where your support hand would touch. Not an issue elsewhere. There are differences in each. eg TangoDown and Magpul XT are virtually same height but TD is more sculpted and less wide so is easier to hold than XT