I just want some opinions. Would it be smarter to EV train stats that a pokemon is already strong in? (i.e. EV train my Alakazam in speed and special attack) or to EV train a pokemon is the stats that he/she lacks (i.e. EV train my Alakazam in HP / Defense)

Depends on the pokemon.

Their Stats

Their Typing

What you wish to do with them.

Alakazam is a special sweeper so sp attk ev's and Speed ev's would be best.

Usually in pokemon you play to a pokemon's strengths.

If you need a wall you go looking for pokemon with the correct typing you need and decent stats for walling.

you don't ev train based on the pokemon so much as what you want it do it and if it would be good at doing it.