The Phanteks G400A is the objective winner of this comparison, securing victory in seven out of eight evaluated specifications. Its most significant advantage over the Lian Li A4-H2O is its maximum cooler height, which is 209% greater. This substantial difference in internal clearance provides the Phanteks G400A with a clear lead in hardware compatibility for larger cooling solutions compared to the Lian Li A4-H2O.

Users prioritizing high-performance cooling hardware should choose the Phanteks G400A for its superior cooler height capacity. Conversely, the Lian Li A4-H2O is the better option for builders who require additional storage density, as it offers a 50% advantage in the number of available 2.5-inch drive bays. Selecting between these two cases depends entirely on whether your build requires more internal space for cooling components or increased capacity for mounting smaller storage drives.