Liquid or Core Aeration
Core Aeration will have a more immediate impact on your soil and the look of your grass. But, the effects are not very long lasting. The Liquid Aeration will have a less immediate impact on your soil, but the effects are longer lasting and cumulative, so your result gets better over time. The exception would be if your soil is very compacted or you have a significant amount of thatch, which would be anything over 1/2 inch. In that case, it is recommend using both Core and Liquid Aeration to help make a long term impact. It's important to have the Core Areation done before the Liquid Aeration. This helps the Liquid Aeration penetrate the lawn more effectively, allowing it to work better and faster.