It may seem rather draconian to some, but I'd have to agree that
vocabulary is the fastest and surest way to know that one is
*definitely* dealing with an individual with effective intelligence,
which isn't the same as having identified someone who *isn't
intelligent* in some other sense, as in fluid ability.
While some persons with low fluid ability can nevertheless have a
strong verbal ability, I've often found that they betray even this
lack of fluid reasoning ability within the span of 2 to 10 minutes of
their conversing on something. The words they tend to pick elicit
their level of comprehension in this regard, even if the specific
vocabulary they use indicates high intelligence w.r.t. vocabulary.
Most notably, their reasoning is sparse, and they often seem to be
relating a wealth of seemingly disjoint and unrelated details and
trivia.
In other words, vocabulary qua communicative ability is the easiest
means to do this in the shortest span of time.
It isn't perfect for all possible scenarios, e.g., certain aspergoid
types or those who think in deviant patterns (they may have a high-
level vocabulary notwithstanding) will not be favored in this
situation, but perfection shouldn't be an object since it is
impossible to achieve.
Writing, I think, would be the best (since speech brings with it
certain barriers even highly intelligent persons may have difficulty
overcoming to varying degrees), but since you've posed the problem in
terms of rapid assessment, conversation would be the optimal
scenario involved.
argumzio