air to air, liquid to air, etc?

For what kind of vehicle?

If you using for cars, you should have liquid / air type. Most of the turbo cars equipped because when the car is idling, the liquid will help to cool it down.

If you using for motorcycle, it may be air/air; but l think the recent new models, they have liquid/air as well. The motorcycle may has less air interference than car (with the hood and other components that block the air way).

l think from a cost & ease of making & installing stand point, air to air is way better. If money is no object & u r pushing some ridiculous amounts of boost, then air to water is the way to go. It really comes down to what the car is used for, how much boost, & how big a turbo u r using. Turbocharged drag cars use air to water because the high boost heats the charge to insane temps & also l thing an air to air inter cooler in the front of the car will mess with the aerodynamics of it too.

As stated before it largely depends on what you're using the vehicle for. If it is a daily driver with only some spirited driving & track days every now & then, an air-air is the best option (and will usually be more than enough for most applications).

Air-water is used more for dedicated vehicles circuirt/drag/track only cars. There r a few reasons for this , firstly the setups r usually more prohibiltively expensive than A-As, but r also less efficient for daily driving. During stop & go traffic air-water intercoolers have a tendancy to ''heat soak'' much faster when not enough air is passing through them, some people use a reserve coolant tank in conjunction with them, but this still does not fully cure the inherent problem.