Neither his inability to speak, who understands his subject but cannot set it forth in words, nor his ignorance, to whom substance is lacking though words abound, can merit commendation; and if I had to choose one of the two, I should prefer uneloquent good sense to loquacious folly.

[Neque infantiam eius, qui rem norit, sed eam explicare dicendo non queat, neque inscientiam illius, cui res non suppetat, verba non desint, esse laudandam; quorum si alterum sit optandum, malim equidem indisertam prudentiam quam stultitiam loquacem]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

De Oratore [On the Orator, On Oratory], Book 3, ch. 35 (3.35) / sec. 142 (55 BC) [tr. Watson (1860)]
    (Source)

(Source (Latin)). Alternate translations:

A Knowledge of Things, without an Ability of expressing them, no more deserves the Name of Eloquence, than a Fluency of Words, join'd to an Ignorance of Things: For my part, were I to take my Choice, I should prefer good Sense, tho' uneloquent, to Nonsense, let it be ever so flowing.
[tr. Guthrie (1755)]

Neither a knowledge of things, without ability to express them, nor a fluency fo words, without ideas, be considered as deserving the name of eloquence: for my part, were I to take my choice, I should prefer good sense, though ineloquent, to nonsense, however flowing.
[Source (1808)]

Neither the ineloquence which cannot impart what it knows, nor the ignorance that is fluent without knowledge, be deemed a subject for commendation; though, if the alternative be unavoidable, I should very much prefer ineloquent information to ignorant loquacity.
[tr. Calvert (1870)]

If have to choose between the two, I would rather have sound common sense without eloquence, than folly with a fine flow of language.
[ed. Harbottle (1906)]

Neither the tongue-tied silence of the man who knows the facts but cannot explain them in language, nor the ignorance of the person who is deficient in facts but has no lack of words, is deserving of praise. And if one had to choose between them, for my part I should prefer wisdom lacking power of expression to talkative folly.
[tr. Rackham (1942)]

No praise is due to the dumbness of the person who has mastered the matter but cannot unfold it in speech, nor, conversely, to the ignorance of the one who does not have the subject matter at his command, but has no lack of words. If we must choose between these alternatives, I myself would prefer inarticulate wisdom to babbling stupidity.
[tr. May/Wisse (2001)]