The best GTX 780 for temperatures is the ASUS Direct CU II Thermal Design. Here is a comparison:
NVIDIA Reference Design GeForce GTX 780 3 GB Card
Temperatures: Idle 37°C, Load 81°C, Load + OC 81°C
ASUS GTX 780 DirectCU II OC 3 GB
Temperatures: Idle 35°C, Load 67°C, Load + OC 68°C
MSI GTX 780 TwinFrozr Gaming 3 GB
Temperatures: Idle 30°C, Load 73°C, Load + OC 76°C
Gigabyte GTX 780 WindForce OC 3 GB
Temperatures: Idle 37°C, Load 72°C, Load + OC 74°C
EVGA GTX 780 Superclocked w/ ACX Cooler 3 GB
Temperatures: Idle 34°C, Load 74°C, Load + OC 76°C