Do you need to use a saddle pad when riding English? Also, which design is better?

A saddle pad is not required, however it's nicer to your horse, and your saddle. The saddle does not allow your horses skin to breathe under it, it traps the heat and sweat and causes discomfort in your horses back. Plus the dirt and sweat on your horse will ruin the leather of your saddle. Using a shaped or regular pad is completely your choice, there's no rules on them. If you are going to show use the white side of your pad.