You do know that there is a radiator at the front transferring heat in an air to water scenario right?
Just do you research online and in current applications and see for yourself.
There are pro's and cons to both and in this 818 application (where the airflow to the intercooler is in question) water to air has a few pro's on its side.
Let's not go on and on here about what's better as its just a foolish argument. They both have their applications and in different scenarios one will have benefits the other hasn't.