A comparison of the regional Fukui index evaluation within the frontier molecular orbital (FMO) Fukui functions is presented. The atoms-in-molecules (AIM) real space-based condensation scheme is compared against a basis set-based condensation scheme and the reliability of the produced reactivity trends is compared. The AIM condensation scheme turns out to give the best results. Furthermore, the AIM atom condensed Fukui indexes can be formally proven to be nonnegative.