When ancient copies of a verse disagree, textual critics lean on a working principle to judge which reading is likely older. Which is it?

The harder reading is often preferred — in the trade's Latin, lectio difficilior potior. The logic: copyists tend to smooth what's rough and soften what's shocking, so the reading a scribe would want to "fix" is more likely the original. It's a guideline weighed against the manuscripts' age and spread, not a trump card.