The simple answer to this question is that it depends on the specific CPU AIO cooler and the layout of your PC case. Some CPU AIO coolers are designed for intake, while others are designed for exhaust. In general, however, most people tend to prefer intake for their CPU AIO coolers.
There are a few reasons for this. First, intake coolers tend to be quieter than exhaust coolers. Second, intake coolers help draw fresh air into the case, which can help improve airflow and cooling performance. And third, many people simply think intake looks better than exhaust (especially if you have a windowed case).
Of course, there are also some downsides to using an intake CPU AIO cooler. One potential issue is that you may end up with dust buildup over time (especially if you don't have good filters in place). Another potential downside is that intakes can sometimes cause issues with positive pressure setups (although this is usually more of a problem with larger cases).
At the end of the day, it's really up to personal preference as to whether you want your CPU AIO cooler to be Intake or Exhaust. If you're not sure which way to go, we recommend doing some research on specific models and seeing what other people have to say about them before making a decision.