The Intel Core i5-9400F is the objective winner of this comparison, securing three spec victories against the Intel Core i5-8400. While the two processors share identical specifications across eleven categories, the Intel Core i5-9400F holds a distinct advantage in its MSRP, which is 14% better than that of its predecessor. This pricing efficiency represents the most impactful difference between the two components, establishing the newer model as the superior value based on the provided data.

Users prioritizing cost-effectiveness should choose the Intel Core i5-9400F, as its improved MSRP provides a clear financial benefit. Because the Intel Core i5-8400 offers no unique spec advantages over the newer model, it remains a viable option only if it can be acquired at a lower cost than the Intel Core i5-9400F. For all other scenarios, the latter is the logical choice given its superior standing in the objective spec-based comparison.