It's good to have a selection of both on your rack, and obey the following. Custom shape the head. Before you place a head, examine the placement and determine if you should shape the head to conform to the seam, pod, or hole. Clean it out. Probably the number-one reason head placements rip out is because climbers fail to properly clean the placement.
Many climbers use a plastic blow tube to blast out debris.
Wire in the back. This orientation protects the cable from getting chewed up, gives you more metal to paste, and minimizes leverage. Drive it deep, then paste it. To place a head, take the pick of your wall hammer and tap the head into the rock. Test a head placement by hitting it directly on the top or bottom with your chisel, trying to make it pivot in the hole.