PVC is a strong vinyl polymer, while HDPE is a thermoplastic polyethylene made from oil. Both pipes are strong even when they are hot. HDPE has been shown to be more durable when failure rates are compared for things like rain, stress, wind, heat, or cold.
Pipes and fittings that are constantly exposed to hot or cold weather slowly get bigger. PVC pipes don't stretch as much as HDPE pipes do.