Question

how do you choose between two characteristics to be used for developing a hierarchy in classification

Answer 1

In a hierarchy at two levels the common characteristics differ a lot between organisms.
Two levels genus and species...species is lower hierarchy so the organisms in same species have different characteristics than two organisms in a genus
still species and genus are related

Answer 2

$\large{ \underline{ \overline{ \mid{ \rm{ \green{Answer:}} \mid}}}}$

The characteristics which is dependent on the previous one and would decide the variety in the next level should be chosen for developing a hierarchy in classification.