The NVIDIA GTX 1660 is the objective winner of this comparison, securing seven spec victories against the five held by the AMD RX 6400. The most significant technical advantage belongs to the NVIDIA GTX 1660, which features a memory bus that is 200% better than its competitor. While the AMD RX 6400 maintains a notable lead in power efficiency, its 56% better TDP is insufficient to overcome the broader hardware superiority demonstrated by the NVIDIA card across the majority of measured categories.

Users prioritizing raw hardware throughput and memory bandwidth should select the NVIDIA GTX 1660 for their system. Conversely, the AMD RX 6400 is the appropriate choice for builders who require a low-power solution and prioritize a superior TDP rating above all other specifications. By aligning these specific advantages with your build requirements, you can ensure that either the NVIDIA GTX 1660 or the AMD RX 6400 effectively meets your unique operational needs.