Regarding functional choice, non-double-hybrid functionals differ only moderately in speed for a fixed basis set, commonly by a factor of two to three between the most and least expensive options. Their accuracy also remains fairly similar (up to 1 kcal/mol differences) when the same basis set is used. By contrast, double-hybrid functionals incur a far greater set selection exerts a stronger influence on both accuracy and computational cost (Figure ). Moving from a double-zeta to a triple-zeta basis set yields a substantial performance boost, whereas further expansion delivers only marginal improvements at a significantly increased cost. Adding diffuse functions consistently improves accuracy both before and after applying BACs while doubling the computational cost, but providing sufficiently large accuracy gains to justify that overhead. This beneficial effect of including diffuse functions is observed in both the Dunning (cc-pVnZ) and Karlsruhe (def2) basis set families, although the later typically offers a more favorable cost-accuracy balance. From these observations, we recommend def2-TZVPD for most applications, with def2-SVPD serving as an efficient alternative in high-throughput workflows. What is more, the effect of BACs on DFT performance proves particularly significant.