What type of intercooler is better? An air to air or an air to liquid?

 

water is a better thermal conductor than air. provided you can keep the water temps down.

 

It depends on your application.

An air-air intercooler is light and simple, and basically requires no maintenance. The efficiency increases with vehicle speed, but will never be over 100%. Found mostly on road race and street cars.

An air-liquid intercooler is heavier and greatly more complex. The efficiency is based on the temperature of the liquid, and can be over 100% if an "ice chest" is used. Found mostly on drag race cars.