Conditions will dictate what pad to take, or even if you need a pad. If you can sleep on deep leaf duff in hardwood forests, you don't need one. If you plan on spending cold nights on the plank floors of the AT lean-to shelters, get the best insulated full length air mattress you can. You have to decide based on cost, durability (many long distance hikers don't like to carry patch kits) and comfort, and generally you only get two of the three.