Accentuative vs. Compensative defensive EV training

Okay, that title's a bit confusing, but it's pretty much the most concise way I can think of to concisely word my question.

Obviously, it's a good idea to buff your Pokémon's HP if you want to make it into a wall. But what I want to know is this: is it better to go with EVs that accentuate your Pokémon's stats, such as giving a Pokémon with higher Def than SpDef extra Def training to make it even more physically defensive, or is it better to give it SpDef training to try and compensate for its relatively low SpDef and thus make it able to tank both types of attacks at the price of not being able to tank physical attacks to its maximum potential?

it's super dependent on which pokemon it is and what you need them to beat. skarmory is a great example. both phys and sdef ev sets are perfectly viable depending on what you're worried about. phys skarmory can better switch into most physical attackers in the tier and is especially useful with rocky helmet or counter. meanwhile, sdef skarm can better check mega fairies (watch out for phys diancie) and latios. so, what do you need? skarmory's typing allows it to tailor its ev spread to its team's needs.

it's boring answer to say "it depends," but it really does. some mons are less versatile and one is usually better than the other--why use hippowdon without phys def evs? to lose to everything it checks?--and in general i think you generally want to play to a mon's stronger defensive statistic, but typing, metagame trends, etc. all play in.