Natural is preferable to artificial . Theoretical justification is also meritorious. So is practicality. In other words, the groups exist in nature. Any classification is unlikely to be either objective or natural if it depends on one or a small set of arbitrarily chosen characteristics.
Phenetic classification uses distance measures and cluster statistics.
Phenetic classification does not depend on any knowledge or hypothesis of phylogeny. Phenetic classification presumes that the organisms, when adequately measured, will tell us how they should be classified. Phenetic classification thus does not concern itself with naturalness. But in practice it remains necessary to choose which and how many characters to measure. Furthermore, there has been no agreement on which statistical tools should be used to identify groupings.